a:ctags_bin calls a batch file that uses %~dp0. Changes include:
- Enable ctags_args to be a list
- Changed default ctags_args to be a list to improve robustness of
s:EscapeCtagsCmd()
- Do not escape 0th argument of ctags_cmd for cmd.exe when it is not
necessary because otherwise batch files may not return expected value
for %~dp0
- Updated tagbar documentation about string and list value types for
ctags_args
See https://github.com/majutsushi/tagbar/issues/133