Find word at caret shortcut

This shortcut was taken from the "Default" RubyMine keymap. It's
similar to "*" in Vim.
Scroll to center shortcut

This shortcut was taken from the "Default for Mac OS X" keymap. It's
similar to "zz" in Vim.
Merge pull request #8 from jcpivotallabs/master

Vim-like shortcuts