Improve handling of "ansi" option in messages (#197, #198)

First, ansi markup in "*args" and "**kwargs" are ignored when used while
"opt(ansi=True)". This caused errors, as such arguments can contains
tags which are not intended to be used as color markups.

Secondly, it strips the color markups present in the "record[message]"
so it can be used somewhere else where the "ansi" context is lost (like
when logs are emitted through socket). Actually, the colors are part of
the handler so it makes sense to strip them from the record.

These change required a whole refactoring of the coloration process. It
has been implemented with optimization in mind: trying to parse the ansi
message only once, then using the generated tokens to colorize the
message appropriately in each handler. It could certainly be improved,
though.

CHANGELOG.rst

@@ -1,7 +1,9 @@
-`Unreleased`
-============
+`Unreleased`_
+=============
 
-- Prevent unrelated files and directories to be incorrectly collected thus causing errors during the `retention` process (`#195 <https://github.com/Delgan/loguru/pull/195>`_, thanks `@gazpachoking <https://github.com/gazpachoking>`_).
+- Prevent unrelated files and directories to be incorrectly collected thus causing errors during the `retention` process (`#195 <https://github.com/Delgan/loguru/issues/195>`_, thanks `@gazpachoking <https://github.com/gazpachoking>`_).
+- Strip color markups contained in ``record["message"]`` when logging with ``.opt(ansi=True)`` instead of leaving them as is (`#198 <https://github.com/Delgan/loguru/issues/198>`_).
+- Ignore color markups contained in ``*args`` and ``**kwargs`` when logging with ``.opt(ansi=True)``, leave them as is instead of trying to use them to colorize the message which could cause undesirable errors (`#197 <https://github.com/Delgan/loguru/issues/197>`_).
 
 
 `0.4.0`_ (2019-12-02)