Added support for double/triple click+dragging.

Now double-click+dragging automatically snaps both ends to word boundaries
(unless on series of spaces), and triple-click selects whole lines.
As a side effect, snapping now occurs on button press, not button release
like it previously was, but I hope that won't be inconvenient for anyone.

Signed-off-by: Christoph Lohmann <20h@r-36.net>
Adding wrap handling in selection.
Implementing 8 bit mode for meta.
There is no 8bit by default and reset 8bit too.
Yes, rs2 != is2.
Removing the overdrawing of some fonts.
Now clipping is more clear.
Fix selecting clearing and BCE

The commit b78c5085f72 changed the st behaviour enabling BCE capability,
that means erase regions using background color. Problem comes when you
clear a region with a selection, because in this case the real mode of the
Glyph is not the value of term.line[y][x], due in drawregion we had enabled
the ATTR_REVERSE bit.

Signed-off-by: Christoph Lohmann <20h@r-36.net>
Removed redundant check in draw code.

We're now clearing empty areas with spaces, so there is no point to check
if character contains non-empty string.

Signed-off-by: Christoph Lohmann <20h@r-36.net>
Fixing the selection issue in altscreens.
Fixing the selection handling to allow one char selection.

Thanks Alexander Sedov <alex0player@gmail.com> for suggesting the fix!
Enable blinking in st.
Be more efficient in blinking.
Add a possibility to modify the string sent by mouse buttons.

Thanks Alexander Rezinsky <alexrez@gmail.com> for the suggestion!
Selection snapping is now considering wrapping.

Thanks Alexander Rezinsky <alexrez@gmail.com> for mentioning this!
Explaining blinking for the dummies.
More stable blinking.
Better comments for the snapping code.
Select to the end of row if end of line is reached.

Thanks Alexander Rezinsky <alexrez@gmail.com>!
Expand the last line with '\n' in case of overselection.

Thanks Alexander Rezinsky <alexrez@gmail.com>!