Merge pull request #2 from tmwilley/backport

Backported from pyrocko to stand-alone

can now skip automatic property initialization with init_props=False

fixed a error introduced in 99cb445c47f6e066041ccea97eae0c5a62dbdf

fixed a problem with storing bool values as attributes

add propnames attribute changed how dicts are serialized

added preliminary Dict class

allow for tuple with arbitrary length

added possibility to serialize arrays as pure lists in yaml

changed how complex numbers are represented in yaml output

operational Choice.T

fixed a problem with loading arrays from xml

more testing

more tests on derived objects

improved SObject