Merge pull request #437 from blipvert/fixes/9

Make x volatile to prevent infinite loop caused by overaggressive optimization
Correct tooltips for add and remove layers
Fixing tooltip mixup between add and remove layers
Merge pull request #439 from tomlechner/master

Fix layers tooltips
Merge pull request #440 from blipvert/fixes/10

Fixed crash in bOpen() when file doesn't exist.
Merge pull request #441 from blipvert/fixes/10

Mark freed argument data v_void so they aren't freed twice.
Added interactive support.
attempt at readline support
More in-depth readline support
Changed USE_READLINE ifdefs to _NO_LIBREADLINE.
Added readline support to configure.