Fixes #75
Merge pull request #80 from vjpr/bug-75

Fixes #75
Implements an option for Environment#precompile to cache paths.

This results in a huge improvement in speed during development.

A performance test is included to check the recompilation is working.
Fixes issue #79.
Merge branch 'precompile-cached-paths' of https://github.com/vjpr/mincer into precompile-cached-paths