Bug fixes and updates.

Fixes jwt construction (#15) and updates to accommodate click 7 (#11).

Preliminary file output.

Preliminary support for file output. (#3)

Add preliminary support for including build products a pre-formatted check outputs. Adding provisional implementation of `cli` components of status app, will likely require later refactoring to support annotation/images. Includes various updates to hook working directory and path resolution to support simple declaration of build products for output upload.

Adds buildkite pipeline running a plugin self-test and reporting via checks api. Expand bats tests with basic coverage of debug/output argument handling.

Expand and fixup tests in `ghapp` layer, cleaning up webhook secret resolution from legacy components and fixing github url parsing.

Closes #1 
Closes #2

First functional release.

v0.0.1

Update README.md