Sort option definitions in ParametricOptions

That should be alphabetical order.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
add --list-features option

Features enabled at build-time could be listed as part of -v option.
However, the output format is not suitable for a program.

This option prints features per line. This may be helpful to write
a test case testing a feature.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
check supported features in unit tests

A unit case can be skipped with this patch.

If a test case requires a .feature of ctags and the target ctags
doesn't support the feature, the test case is automatically skipped.

Features required by a unit test case must be listed in
Units/TEST/features. Features supported in a ctags file can
be listed with --list-features option.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
don't run conflib-recursive.d test if option-directory is not supported

Currently scandir is used to load options under a directory.  Some
platform doesn't have scandir. On such platform, a unit test requires
option-directory feature should be skipped.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>