Implement "match" delimitedtext for ad hoc motions

This is a future Vim feature. Use e.g. 'vam*' to select everything
between matching '*' chars.

The patch is described in
https://groups.google.com/forum/#!searchin/vim_dev/im%2420am/vim_dev/pZxLAAXxk0M/wdOgpOQ05Z8J

Also discussed in #335.
Implement "match" delimiterholder for surround.

This implements "m<char>" for the surround plugin.

It allows for quick one-off surround operations, e.g. "yswm*" will
surround the next word with asterisks. "csm*m%" will then in turn
replace them with percent characters.
Merge pull request #390 from albertdev/match-adhoc-delim

Implement "Match ad hoc delimiter"