Moved Doxygen comments from source files to public headers.
Added public header service.h to the project and library targets.
Changed AFC function return types to afc_error_t to match headers.
Converted error types from int16_t to typedef'ed enums.

This commit changes the binary API. 16-bit error types
can be retained by defining LEGACY_ERRORS.
Merge branch 'enum-errors'
Merge branch 'doxygen'

Conflicts:
	include/libimobiledevice/service.h
	src/afc.c
	src/restore.c
	src/service.c