api: fix 'kallithea-api --save-config'

Commit eca0cb56a822 attempted to fix a type inconsistency, which caused
failure in the 'kallithea-api' tool when using '--save-config', but this
unfortunately did not fix the problem completely.

Following error still appeared:

Traceback (most recent call last):
File ".../bin/kallithea-api", line 33, in <module>
sys.exit(load_entry_point('Kallithea', 'console_scripts', 'kallithea-api')())
File ".../bin/kallithea_api.py", line 84, in main
'apihost': args.apihost})
File ".../bin/base.py", line 104, in __init__
self.make_config(config)
File ".../bin/base.py", line 132, in make_config
ext_json.dump(config, f, indent=4)
File "/usr/lib/python3.7/json/__init__.py", line 180, in dump
fp.write(chunk)
TypeError: a bytes-like object is required, not 'str'

The json module documentation says:
https://docs.python.org/3.7/library/json.html#basic-usage
"The json module always produces str objects, not bytes objects. Therefore,
fp.write() must support str input."

Therefore, instead of opening the file in binary mode and writing bytes,
open it in text mode and write strings.

For symmetry reasons, we make the same change when _loading_ the config
file, but this code worked regardless.

py3: fix rc_types error

Spotted by pytypes:

File "kallithea/bin/base.py", line 133, in make_config: Function BinaryIO.write was called with the wrong arguments [wrong-arg-types]
Expected: (self, s: Union[bytearray, bytes, memoryview])
Actually passed: (self, s: str)

py3: migrate from urllib2 to urllib

Based on 2to3 urllib, but with unnecessary imports removed.

py3: support __bool__

From 2to3 -f nonzero.

lib: clean up ext_json and how it is used - avoid monkey patching

Note that py3 json.dumps will return ASCII (with all unicode escaped) encoded
as str. But we generally want JSON as bytes (which json.loads also can read),
so also wrap the result with ascii_bytes in many places.

codingstyle: trivial whitespace fixes

Reported by flake8.

bin: fix __eq__ of bin/base.py RcConf

__eq__ without parameter makes no sense - found by pylint.

(The method is thus apparently unused and could be removed completely together
with other RcConf code.)

cleanup: consistently use 'except ... as ...:'

Use the Python 2.6+ syntax instead of the old confusing 'except ..., ...'
syntax.

Correct licensing information in individual files.

The top-level license file is now LICENSE.md.

Also, in various places where there should have been joint copyright holders
listed, a single copyright holder was listed. It does not appear easy to add
a link to a large list of copyright holders in these places, so it simply
refers to the fact that various authors hold copyright.

In future, if an easy method is discovered to link to a list from those
places, we should do so.

Finally, text is added to LICENSE.md to point to where the full list of
copyright holders is, and that Kallithea as a whole is GPLv3'd.

Second step in two-part process to rename directories.
This is the actual directory rename.