Fix name of PKG_CHECK_MODULES test for limd 1.1.5

The result of the second PKG_CHECK_MODULES(libimobiledevice11, ...) was
read out of cache and succeeded on systems with libimobiledevice-1.0 >=
1.1.0 but << 1.5.0.  Giving it another unused name fixes this.

Signed-off-by: Loïc Minier <lool@dooz.org>
Use PKG_CHECK_EXISTS() and not PKG_CHECK_MODULES()

PKG_CHECK_MODULES() defines a bunch of variables and might use cached
information if the same name is used multiple times.  Use the more
correct PKG_CHECK_EXISTS().

Signed-off-by: Loïc Minier <lool@dooz.org>
Use bundle identifier of official VLC app in README
Update README with latest information and URLs
Add experimental support for "st_birthtime" on darwin
Bump version to 1.1.3