new tweak for "renderer_tweaks"

[Alexey-T]

I am working on adding a new option which makes optimization on rendering complex syntax-colored texts.

i see it gives boost with this complex file.
many-tokens.zip

it's fake content, can be tested in several lexers: C, Python, Bash.
the main property of this file: big count of lexer tokens per each line.
here I see boost 80% on Linux gtk2.
on Windows: did not test (maybe gain will be very small, win32 API TextOut is much faster).

I tested this via option "log_timing": true .

but optimization gives no gain on small/average files.
anybody needs it?