tss.vim: TSSstructure menu; TSSfile open project file

- change `TSSstructure` to popup nagivation menu
- add `TSSfile`: quickly open project files, with filename completion
- use TSSupdate nocheck in TSSshowErrors
tss.vim: TSSfilesMenu - open project files via menu
tss.vim: add sample keymap
add tests: issue #17, concat-map
tss.vim: guard against tss not running/no python
tss.vim: only use shell on windows; fixes #18
bump build number