Model descriptions serialization

[shuttle1987]

Related to #154

As it stands the model descriptions are made in an ad-hoc format:

persephone/persephone/rnn_ctc.py

Lines 18 to 24 in aa69575

	def write_desc(self):
	""" Writes a description of the model to the exp_dir. """
	path = os.path.join(self.exp_dir, "model_description.txt")
	with open(path, "w") as desc_f:
	for key, val in self.__dict__.items():
	print("%s=%s" % (key, val), file=desc_f)

I propose that we make this a more easily parseable format when we write this to a file.

I'm thinking something like YAML or JSON works well here. Is there a preference for serialization format?

JSON comes in the standard library but has a bit less flexibility. That said flexibility isn't necessarily a benefit here.

[shuttle1987]

Using Keras will really fix this properly, but I think we have done enough as of the changes in PR #197 to close this issue.