Collected fundamental operation optimizations

[mborland]

Lots of short circuiting, and the revitalization of direct initialization help us significantly.

Benchmarks at current head:

===== Comparisons =====
comparisons<float        >: 69376      us (s=299999985)
comparisons<double       >: 48137      us (s=299999985)
comparisons<decimal32_t  >: 1121819    us (s=299999985)
comparisons<decimal64_t  >: 1050653    us (s=299999985)
comparisons<decimal128_t >: 2100040    us (s=299999985)
comparisons<dec32_fast   >: 457808     us (s=299999985)
comparisons<dec64_fast   >: 425689     us (s=299999985)
comparisons<dec128_fast  >: 418523     us (s=299999985)

===== Addition =====
Addition<float        >: 11427      us (s=18446744073609551621)
Addition<double       >: 12095      us (s=18446744073609551621)
Addition<decimal32_t  >: 1531348    us (s=1346704632194777589)
Addition<decimal64_t  >: 1337036    us (s=15185976904076359728)
Addition<decimal128_t >: 2449492    us (s=343379103667783520)
Addition<dec32_fast   >: 920156     us (s=1346704632194777589)
Addition<dec64_fast   >: 891290     us (s=15185976904076359728)
Addition<dec128_fast  >: 889484     us (s=343379103667783520)

===== Subtraction =====
Subtraction<float        >: 14211      us (s=18446744073659548966)
Subtraction<double       >: 13689      us (s=18446744073659548961)
Subtraction<decimal32_t  >: 1643943    us (s=4059123726101601672)
Subtraction<decimal64_t  >: 1372428    us (s=13628957610294930046)
Subtraction<decimal128_t >: 2384365    us (s=15500212624985615725)
Subtraction<dec32_fast   >: 940396     us (s=4059123726101601672)
Subtraction<dec64_fast   >: 925618     us (s=13628957610294930046)
Subtraction<dec128_fast  >: 909737     us (s=15500212624985615725)

===== Multiplication =====
Multiplication<float        >: 12198      us (s=18446744073609551621)
Multiplication<double       >: 12243      us (s=18446744073609551621)
Multiplication<decimal32_t  >: 1955406    us (s=13282323798186187586)
Multiplication<decimal64_t  >: 2352767    us (s=8272959584202096614)
Multiplication<decimal128_t >: 6896256    us (s=17382535922206154208)
Multiplication<dec32_fast   >: 1943814    us (s=13282323798186187586)
Multiplication<dec64_fast   >: 2340795    us (s=8272959584200780119)
Multiplication<dec128_fast  >: 6164829    us (s=17382535922206154208)

===== Division =====
Division<float        >: 13860      us (s=889346465)
Division<double       >: 17921      us (s=889346420)
Division<decimal32_t  >: 2699644    us (s=11972246100944077518)
Division<decimal64_t  >: 5588538    us (s=11051429967436580468)
Division<decimal128_t >: 10425350   us (s=5185696363361324687)
Division<dec32_fast   >: 2003501    us (s=11972246100944077518)
Division<dec64_fast   >: 5246047    us (s=11051429967436580468)
Division<dec128_fast  >: 8066989    us (s=5185696363361324687)

This PR:

===== Comparisons =====
comparisons<float        >: 62805      us (s=299999985)
comparisons<double       >: 38461      us (s=299999985)
comparisons<decimal32_t  >: 929050     us (s=299999985)
comparisons<decimal64_t  >: 914809     us (s=299999985)
comparisons<decimal128_t >: 2015205    us (s=299999985)
comparisons<dec32_fast   >: 462219     us (s=299999985)
comparisons<dec64_fast   >: 429917     us (s=299999985)
comparisons<dec128_fast  >: 420875     us (s=299999985)

===== Addition =====
Addition<float        >: 11861      us (s=18446744073609551621)
Addition<double       >: 12219      us (s=18446744073609551621)
Addition<decimal32_t  >: 1025441    us (s=1346704632194777589)
Addition<decimal64_t  >: 769356     us (s=15185976904076359728)
Addition<decimal128_t >: 1411218    us (s=343379103667783520)
Addition<dec32_fast   >: 633930     us (s=1346704632194777589)
Addition<dec64_fast   >: 562879     us (s=15185976904076359728)
Addition<dec128_fast  >: 660342     us (s=343379103667783520)

===== Subtraction =====
Subtraction<float        >: 11977      us (s=18446744073659548966)
Subtraction<double       >: 12487      us (s=18446744073659548961)
Subtraction<decimal32_t  >: 1049595    us (s=4059123726101601672)
Subtraction<decimal64_t  >: 830560     us (s=13628957610294930046)
Subtraction<decimal128_t >: 1431588    us (s=15500212624985615725)
Subtraction<dec32_fast   >: 680528     us (s=4059123726101601672)
Subtraction<dec64_fast   >: 633662     us (s=13628957610294930046)
Subtraction<dec128_fast  >: 722225     us (s=15500212624985615725)

===== Multiplication =====
Multiplication<float        >: 11891      us (s=18446744073609551621)
Multiplication<double       >: 12303      us (s=18446744073609551621)
Multiplication<decimal32_t  >: 1940743    us (s=13282323798186187586)
Multiplication<decimal64_t  >: 2047288    us (s=8272959584202096614)
Multiplication<decimal128_t >: 5014345    us (s=17382535922206154208)
Multiplication<dec32_fast   >: 1415591    us (s=13282323798186187586)
Multiplication<dec64_fast   >: 1845096    us (s=8272959584202096614)
Multiplication<dec128_fast  >: 4613134    us (s=17382535922206154208)

===== Division =====
Division<float        >: 12842      us (s=889346465)
Division<double       >: 17151      us (s=889346420)
Division<decimal32_t  >: 2499043    us (s=11972246100944077518)
Division<decimal64_t  >: 5066342    us (s=11051429967436580468)
Division<decimal128_t >: 9784609    us (s=5185696363361324687)
Division<dec32_fast   >: 1942231    us (s=11972246100944077518)
Division<dec64_fast   >: 5256758    us (s=11051429967436580468)
Division<dec128_fast  >: 8143953    us (s=5185696363361324687)