Create an install target

[linas]

I want to add MCP to some existing servers, and to do that, it seems that a shared library plus installed header files are needed. This change allows sudo make install to run, giving

Install the project...
-- Install configuration: "Release"
-- Installing: /usr/local/lib/libmcp.so.2024.11.5
-- Installing: /usr/local/lib/libmcp.so.1
-- Installing: /usr/local/lib/libmcp.so
-- Installing: /usr/local/include/mcp/mcp_client.h
-- Installing: /usr/local/include/mcp/mcp_message.h
-- Installing: /usr/local/include/mcp/mcp_resource.h
-- Installing: /usr/local/include/mcp/mcp_server.h
-- Installing: /usr/local/include/mcp/mcp_tool.h
-- Installing: /usr/local/include/mcp/mcp_stdio_client.h
-- Installing: /usr/local/include/mcp/mcp_sse_client.h

This delta was created with claude, I have not yet tested to see if it "did the right thing", but so far, it looks OK to me ...

[linas]

well, apparently this fails to install the needed files mcp_thread_pool.h and json.hpp ... which I just now fixed.