Issue #130: Fixed support for indenting by tab
Allow indent a block of code by selecting a range of lines
and pressing 'tab'. The behavior implemented is the same as
the one in Sublime Text editor since I found it intuitive enough.
/* XPM */
static char *mac_left_xpm[] = {
/* width height ncolors chars_per_pixel */
"14 14 7 1",
/* colors */
"a c white",
"b c #555555",
"c c #aaaaaa",
"d c #cccccc",
"e c #333366",
"f c #666666",
"g c none",
/* pixels */
"aaaaaaaaaaaaab",
"addddddedddddb",
"adddddeedddddb",
"addddecedddddb",
"adddecceeeeedb",
"addecccccccedb",
"adeccccccccedb",
"adeccccccccedb",
"addecccccccedb",
"adddecceeeeedb",
"addddecedddddb",
"adddddeedddddb",
"addddddedddddb",
"fffffffffffffb",
};