Merge pull request #150 from zzak/master

BigDecimal Documentation, Thx zzak.
add tests to test the behavior of State::configure (and its alias State::merge).
fix some bugs in the C versions of State::configure and add the alias in the Java version.
add merge alias for configure in jruby
Use len for return values
Change the CHANGES
Remove unnecessary GET_STATE(self) to avoid an unused-but-set-variable warning in gcc 4.6.
Merge pull request #153 from shugo/master

Remove unused variable
Increase hash likeness of State objects
Prepare version 1.7.6