Initial support for using mettle as a shared lib
Split out compiled_suite stuff into its own file
Move some headers into include/mettle/matchers, since they are only used for matcher-related stuff
Move file_runner code to src/
Move forked_test_runner to src/libmettle
Move scoped_pipe.hpp to src/
Move child and pipe logs to src/
Allow term.hpp to be used in multiple translation units