kc: added support for transactions

Closes #2.
kc: added Size function
kc: implement match_prefix function using C

Using C so the code don't look too ugly. This function wraps
kcdbmatchprefix function.
kc: added MatchPrefix method to DB type
kc: simplify test for MatchPrefix
kc: don't call make if kcdbmatchprefix return 0 elements

I believe that gc won't allocate anything, but let's just protect it :-)
kc: implement match_regex function in C

This function is like match_prefix, but wraps kcdbmatchregex.
kc: added MatchRegex method to DB type