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 *CheckOn10_xp_xpm[] = {
/* width height ncolors chars_per_pixel */
"10 10 2 1",
/* colors */
"a c #21A121",
"b c none",
/* pixels */
"bbbbbbbbbb",
"bbbbbbbbbb",
"bbbbbbbbab",
"bbbbbbbaab",
"bbabbbaaab",
"bbaabaaabb",
"bbaaaaabbb",
"bbbaaabbbb",
"bbbbabbbbb",
"bbbbbbbbbb",
};