Adding `VCMergeConflictCheck` for detecting unresolved merge conflicts in code.

Closes: #76
Merge pull request #91 from Mobius5150/merge_conflict_check

Adding `VCMergeConflictCheck` for detecting unresolved merge conflicts i...
Optimizing the VIPRestrictedCommandsCheck.

Using `strpos()` to see if file contains restricted keywords before applying the regular expression. Over 20 runs this reduced the average time for running just this check by 50%.

Also removing unused variable `$error`.
Merge pull request #94 from Mobius5150/master

Updating plugin version number and changelog.
Syncing README.txt with README.md

README.txt was out of date from the updated contents of README.md.

Also updated the stable tag and tested up to tag so that we can push changes to WordPress.org.
Merge pull request #95 from Mobius5150/patch-1

Syncing README.txt with README.md
Merge pull request #96 from Mobius5150/optimizations

Optimizing the VIPRestrictedCommandsCheck.