minor fix in muffin.1 manpage (hyphen-used-as-minus-sign)
Remove generated files from versioning
Fix warning about using uninitialized variable

This allows run higher optimization level along with -Werror flag
drop libmuffin dependency of testasyncgetprop and testboxes

Since part tested in testasyncgetprop and testboxes will not be exported in
of libmffin ABI anymore, the test programs are compiled with the relevant
source directly, not linked against libmuffin library.
Define the macros LOCAL_SYMBOL and API_EXPORTED

This 2 macro define the ELF visibility of a symbol:
 - LOCAL_SYMBOL: define with __attribute__ ((visibility ("hidden")))
 - API_EXPORTED: define with __attribute__ ((visibility ("default")))
Under normal circumstances, the second does nothing but it is provided for
consistency and has an effect if later compiler flag -fvisibility=hidden is
passed. If the compiler does not understand the visibility attribute, the
macros are defined to nothing.
Hide private symbols from the libmuffin ABI

All private symbols have been declared with the LOCAL_SYMBOL macro.
This set the ELF visibility of the symbol to hidden.
Merge branch 'hide-local-symbols' of https://github.com/nbourdau/muffin into nbourdau-hide-local-symbols

Conflicts:
	src/core/screen.c