Proper handling of dead keys

Several input methods use `\` as a dead key to print ASCII characters. 

This causes problems when multiple backslashes are involved: `\\` should print as `\` and not affect future characters, but in practice the keystroke sequence `\\n` ends up printing `n` (with the `\\` collapsed into a single `\`).

The changes made to `jquery.ime.js` fix this by clearing the context after a dead key sequence is typed. 

I have also edited all the input methods using such dead key sequences (that I could find) and added tests for them.