Merge pull request #4 from esben/master

Conditional ops (set_if, append_if, prepend_if), Bool, Int, Float and List types, and a minor String improvement
Add tests for internal value contamination in List

Test for contamination of stored value when applying amend functions.
Fails for remove and extend.

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Fix value contamination for List remove and extend amends

Signed-off-by: Esben Haabendal <esben@haabendal.dk>