- add Fl::args_to_utf8() to convert commandline arguments to UTF-8
This new function closes the gap that previously only Visual Studio
applications converted their commandlines to UTF-8.
Tested with MinGW, MSYS2/MinGW-w64, and Visual Studio (2019).
- remove obsolete svn '$Id$' tags from all source files
- update .fl files and generated files accordingly
- replace 'http://www.fltk.org' URL's with 'https://...'
- replace bug report URL 'str.php' with 'bugs.php'
- remove trailing whitespace
- fix other whitespace errors flagged by Git
- add and/or fix missing or wrong standard headers
- convert tabs to spaces in all source files
The only relevant code changes are in the fluid/ folder where
some .fl files and other source files were used to generate
the '$Id' headers and footers.
