* dumping doesn't work at CT
* timestamps don't work at CT
* aliases don't work at CT
* renamed tserialization -> tnative to mirror rename of native.nim file
* added comptime tests to tnative, currently only execute when doing
nim nativeTests, because of compiler bug
* Fixes#70, #91
* moved load procs to yaml/loading.nim
* moved input YamlStream into ConstructionContext
* made ConstructionContext a non-ref object
* harmonized code style & comments
* renamed yaml/serialization.nim to yaml/native.nim
* allow '!' at beginning of tag URI in %TAG directive
* recognise \t as start of more indented line in block flow scalar
* Made testEventParser more robust