Merge pull request #126 from rupnikj/TStr

TStr unit tests
Len and CStr() now call empty
Merge branch 'TStr' of https://github.com/qminer/qminer into TStr
fix, added some tests
Merge pull request #127 from lstopar/TStr

T str
Merge branch 'TStr' of https://github.com/qminer/qminer into TStr
tests, trunc fix (getsubstr now thros an exception)