caps: Rename to features to avoid confusion
caps: Rename the enum name too!
features: Rename `_HAS_` to `_FEATURE_`
Merge pull request #2150 from libgit2/vmg/features

caps: Rename to features to avoid confusion
Fix the description for `GIT_FEATURE_SSH`.
Merge pull request #2151 from arthurschreiber/patch-3

Fix the description for `GIT_FEATURE_SSH`.