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 *RadioOn_w95_xpm[] = {
/* width height ncolors chars_per_pixel */
"12 12 5 1",
/* colors */
"a c black",
"b c #808080",
"c c #DFDFDF",
"d c white",
"e c none",
/* pixels */
"eeeebbbbeeee",
"eebbaaaabbee",
"ebaaddddaade",
"ebaddddddcde",
"badddaadddcd",
"baddaaaaddcd",
"baddaaaaddcd",
"badddaadddcd",
"ebaddddddcde",
"ebccddddccde",
"eeddccccddee",
"eeeeddddeeee",
};