Merge pull request #2975 from andyli/travis

Reducing the size of build matrix.
optimize python Vector (no bound checks), add vector iteration test
minor array implementation performance improvements
inline and optimize TArray expressions when possible
optimize tarray read access further and do some cleanup
inline some string methods
add toplevel completion, resolve positions for position/usage completion (closes #327, closes #569)
[TravisCI] Put library tests into separate "TEST=third-party" build.