* Replaced all assert statements with yAssert, which prints an error message
and quits on failure, but does nothing when compiling with -d:release.
* Implemented and used internalError for better discovery of internal bugs.
Fixes#8.
* Made RawYamlStream able to raise YamlStreamError, which might primarily be
useful for user-defined serialization
* Properly encapsulate RangeError coming from int/uint serialization on 64bit
machines in YamlStreamError.
* Some minor style improvements