Remove call to ord in lib3 emitter code

[scauligi]

Fixes issue #118
encode produces a bytestring, and iterating over a bytestring in python 3 produces ints instead of chars

[perlpunk]

I vote for merging. @ingydotnet @sigmavirus24 or anyone else, thoughts?

[ingydotnet]

Can we get a test to support this change?

[perlpunk]

Here's a test reproducing it:

import yaml

l = lambda: None
d = yaml.dump({ 'l': l }, default_flow_style=False)

print(d)
assert(d == "l: !!python/name:__main__.%3Clambda%3E ''\n")

Currently it produces an exception in python3:

...
  File "lib3/yaml/emitter.py", line 607, in prepare_tag
    chunks.append('%%%02X' % ord(ch))
TypeError: ord() expected string of length 1, but int found

[perlpunk]

merged in d13a3d0