Flymake support for indicating errors in margin

Flymake support for indicating errors in margin

Add optional support for display flymake error in margin,
this allow displaying error indicators in both graphical and
terminal frames.
* doc/misc/flymake.texi (Customizable variables)
(Flymake error types): Document new margin indicator.
* etc/NEWS: Announce the new Flymake user option for margin
indicators.
* lisp/progmodes/flymake.el (flymake-indicator-type)
(flymake-margin-indicators-string, flymake-autoresize-margins)
(flymake-margin-indicator-position): New user options.
(flymake--original-margin-width): Add buffer-local variable for
store original buffer margin width.
(flymake-error, flymake-warning, flymake-note): Use new margin
value.
(flymake--indicator-overlay-spec): Rework and Rename from
flymake--fringe-overlay-spec.
(flymake--resize-margins): Add new function for resize margin
width.
(flymake--highlight-line, flymake-mode): Rework.