Don't switch to input mode on click to radio button.

If a radio button was clicked vimb switched to input mode. Now the logic what
element is editable is consistent within dom.c. Editable are textarea, and
input elements without any type a and type text or password.
Added noted about gvim -f option as editor-command (#141).
Add Void Linux package to README.
Fixed duplicate shown showcmd in command mode.

If <C-R> was pressed within the inputbox, the showcmd section of the statusbar
showed ^R^R instead of a single ^R.
Add :reg[ister] command to show register contents.
Removed unneeded key in ex cutbuf.
Fixed none complete keysequence on "<Esc>.

If " is typed in normal mode vimb expects a register char so that the " is
show in showcmd section of the statubar. All following next none register
chars are appended to the key sequence so that the command is not ready to
performed.
This patch switch back to starting parser state if the char after the " is no
valid register.
Allow select of yank buffer for ;y hinting (#151).
Renamed cutbuf variables and constants to reg.
Fixed missed uri escaping for '+' (#152).