fix for PAM files when writing RGB, conversion RGB16->24/32

PAM writing for all RGB formats was broken (wrong max value of 256, it is in fact 255).

Also, conversion from RGB16 to RGB24 or RGB32 was also wrong due to a typo.
Merge pull request #120 from hwhw/fix-screenshot

fix for PAM files when writing RGB, conversion RGB16->24/32
add go back/forward method for credocument
Merge pull request #121 from chrox/master

add go back/forward methods for credocument
fix segmentation on CJK characters when updating selection
Merge pull request #122 from chrox/master

fix segmentation on CJK characters when updating selection
add getTextFromPositions method for credocument
set larger range of font sizes for credocument
Merge pull request #123 from chrox/master

add getTextFromPositions method for credocument
fix highlight offset in scroll mode
Merge pull request #124 from chrox/master

fix highlight offset in scroll mode
Add a os.execute-like function for calling execl

It is safer than using os.execute when passing filenames as arguments
Merge pull request #125 from thotypous/master

Add an os.execute-like function for calling execl
Better error handling on execl
Merge pull request #126 from thotypous/master

Better error handling on execl
Update LuaJIT to latest stable
Merge pull request #127 from thotypous/master

Update LuaJIT to latest stable
add getLinkFromPosition method for cre backend
Merge pull request #128 from chrox/master

add getLinkFromPosition method for cre backend
fix line wrap at punctuation apostrophe