Adds an ifdef to check minimum vim version.

Currently no warning is shown. Showing a warning here would case Vim to pause on
'Press ENTER or type command to continue'.
Adds minimum requirements to docs.
Merges branch 'feature/add-minimum-version-ifdef' into develop
Bumps version to 0.1.12
Updates changelog.
Build 0.1.12
Merges branch 'release/0.1.12' into develop