streak-mode multibyte highlighting

[justinmk]

sneak basic mode works fine with all multibyte situations so far.

however, streak-mode has the same issue that easymotion has or had: easymotion/vim-easymotion#28

Target labels are offset or missing completely. To test, try a streak-mode search for ïo (on a Mac, option-o + o) in the following text:

foo æfïooæ ïoòôõïo ïofoo fooïo ïoïo

Another test case (#47):

абв

Another thing to keep in mind with sneak basic mode:

• use strwidth() instead of len() (vim-7.3 only)

see also: easymotion/vim-easymotion#60

[justinmk]

This is fixed now. 😎