Now using the same pattern as Go's http package.
- the `compiler.Compiler` struct can be used directly (and tests to do
to avoid messing with the global version)
- `compiler.DefaultCompiler` contains a public default Compiler instance
- `compiler` exposes proxy functions (e.g. Compile) back to the
DefaultCompiler
Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>
