add 'return' support (#3)
add combine support (#3)
add 'return!' support (#3)
add 'let!' support (#3)
add 'use!' support (#3)
add try-with support (#3)
add try-finally support (#3)
add failure computation expression support (#3)
add zero support to 'with zero' computation exprs (#3)
add base class to 'with zero' builders (#3)
add loop support to 'with zero' builders (#3)
Merge pull request #6 from bleis-tift/result-computation-expression

add support result computation expressions

#3