Makefile: completly rewrite

Makefile: completly rewrite

This change is a complete rewrite of fscrypt's Makefile.

The new build rules can be roughly divided into secions:
  Build   - bin/fscrypt and bin/pam_fscrypt
  Linting - gen (for .proto files), format, lint
  Test    - test, test-{setup|teardown}, coverage.out
  Install - install, uninstall, install-{bin|pam}
  Tools   - tools and other bin/* needed for the other rules

As before, "make" builds the binary and pam_module, while "make all"
builds and tests everything (except for integration tests), and "make
clean" removes any generated files.

Also note that this new build system:
  - Doesn't require input_fail.py
  - Properly falis on linter errors
  - Builds everything into the bin/ directory (customizable)
  - Builds all the vendored tools