Mod support for all Keypress.

[robinvd]

Changes:

• Keypress to allow mods for every type except unknown
• Changes to slate to convert them
• Changes to Vim to ignore mods on keybindings that did not have mods before

Will look into adding things from Vty tomorrow.

[robinvd]

Changed what you recommended, added keys from Vty and made some examples for them.

[ChrisPenner]

Looks great! ✨ 👍 ✨