Update next version plan to 2.0.0

In order to better high-light the name change, and
backwards incompatibility.

This also allows dependent tools (like flake8) to
pin to `pycodestyle < 2.0` as a dependency while
transitioning to the new package.

Author: IanLee1521

CHANGES.txt

@@ -2,7 +2,7 @@ Changelog
 =========
 
 
-1.8.0 (unreleased)
+2.0.0 (unreleased)
 ------------------
 
 Announcements:

pycodestyle.py

@@ -64,7 +64,7 @@
 except ImportError:
     from ConfigParser import RawConfigParser
 
-__version__ = '1.8.0.dev0'
+__version__ = '2.0.0.dev0'
 
 DEFAULT_EXCLUDE = '.svn,CVS,.bzr,.hg,.git,__pycache__,.tox'
 DEFAULT_IGNORE = 'E121,E123,E126,E226,E24,E704,W503'