Don't recursively map all the time

If users remap keys, the behaviour of the things set up in vimrc may change.

An example of this is the common remapping to switch `;` and `:`, which will
cause all of the keyboard shortcuts involving `:` to fail. Switching the *map
statements to their *noremap counterparts fixes this problem, by using the
original meanings.
Merge pull request #158 from ElliottH/mapping

Don't recursively map all the time
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