Various: Minor improvements.

- Awk: Added menu separators to "Comments" and "Run".
- Bash: Fixed the priority of the "Tools" menu entry,
  was conflicting with Awk.
- Latex: Mapleader issues fixed.
C-Support: Extended the documentation.

- Documented the option 'g:C_CreateMenusDelayed'.
- Added issue "The plug-in loads slowly." to "Troubleshooting".