Support Postgres 16

[fboulnois]

A number of changes to improve the extension:

• Add unit tests
• Include mechanism to build, test, and benchmark code
• Support Postgres 16 (closes #14 )
• Remove shared_preload_libraries requirement (closes #16 )
• Refactor the sql so it lives in its own directory
• Build the extension for Postgres 13 and later
• Refactor extension code so that timestamp and random data are added sequentially and data is not overwritten (partially addresses #15 )
• Update the benchmarks with the latest version of the extension
• Bump the extension to 1.3.0