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 *CheckOnColor_xpm[] = {
/* width height ncolors chars_per_pixel */
"16 16 3 1",
/* colors */
". c none",
"* c black",
"b c red",
/* pixels */
"............bbbb",
"...........bbbbb",
"..........bbbb*.",
".........bbbb*..",
"........bbbb*...",
".......bbbb*....",
".......bbbb*....",
"bb....bbbb*.....",
"bbb...bbbb*.....",
".bbbbbbbb*......",
"..bbbbbbb*......",
"...bbbbbb*......",
"....bbbb*.......",
"....bbb*........",
".....bb*........",
".....bb*........",
};