rewrite for TSv0.9.x
follow "definition" JSON change in TSSdef()
for debugging: record last error stack trace
support getReferencesAtPosition
tss.vim: always use new preview window for docs
tss.vim: slightly improved log-file handling
fix #7 (update); add test coverage
support reduced completion output (#6)

- completions-brief does not fill in entry details
- completions does now pre-filter entries against existing prefix
- test coverage added
tss.vim: fix trace bug; remove old comment
tss.vim: set omnifunc only for .ts files
tss.vim: improve update handling
update README before merge
add CHANGES.txt