Reset after jump documentation fix

In my branch I made 3 changes:

- Fixed a variable name in the documentation to reflect the actual variable name (g:mediummode_allowed_motions vs. g:mediummode_allowed_character_motions)
- Changed the plugin to allow a reset of the character count after a jump command by comparing the column and line-number where the jump was triggered with the current line and column number (if it's changed, then reset the character count [e.g., assume a jump])
- Get rid of the `echo ''` in the s:MediumModeResetCount function that was causing me to have to hit enter to open up a new buffer in the current session

This is one of my first stabs at any Vimscript so if you find something to be non-performant or flat-out stupid I definitely won't be offended.

Awesome plugin by the way :)