FEAT: improved terminal support on posix platforms

Now unicode input is (somehow) supported and there are new key shortcuts for clearing line (CTRL-U and CTRL-K) and navigation skipping by words (OPTION key with left or right arrow)

Known issues:
When TAB is entered, the line navigation using left/right arrows and char deletion is wrong. Any idea how to fix it without disabling TAB-ed input?

Note:
Few lines of code were taken from Brian Dickens' Ren-C