Update to vimb-2.5.

Changes:
Main features:
- Support for HTTP Strict Transport Security (HSTS)
- Added support for URI handler to spawn custom programs depending on
  protocol. Thanks to Samuel Archer who implemented this for us.
- Added completion for :handler-remove and :shortcut-remove commands
- Support for different yank registers and readonly registers like in vim
- Allow to escape % with \ in expanded commands
- Allow to use \\$ to input \$
- Save current URI in $VIMB_URI for spawned shell commands
- Save xid and pid in the environment $VIMB_XID and $VIMB_PID
- Added some automated test to check vimb
- Allow shortcut parameters to contain spaces

Fixes:
- Switch back to normal mode if inputbox is cleared like vim
- Cleaned up the code, remove unneeded macros
- Use central expansion logic for the ex commands as well as the download
  processing
- Don't tuch history file if history size is 0
- Check second key for z{x} that caused ever zx with x not in "ziI" to zoom
  out
- Changed the default user agent to more common format that allows to use google