Fixed bug where preparse() wasn't called before parsing

[tleonhardt]

Deleted postparse() since it was redundant with postparsing_precmd()
- Decided to keep postparsing_precmd() because of its more self-documenting name

• Removed reference to postparse() in the docs

This partially addresses #417

[codecov]

Codecov Report

Merging #420 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #420      +/-   ##
==========================================
+ Coverage   88.94%   88.97%   +0.02%     
==========================================
  Files           9        9              
  Lines        2678     2676       -2     
==========================================
- Hits         2382     2381       -1     
+ Misses        296      295       -1

Impacted Files	Coverage Δ
cmd2/cmd2.py	90.32% <ø> (+0.05%)	⬆️

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[tleonhardt]

As long as everyone is happy with how I handled this issue, then this is the last thing I wanted to get in before we do a 0.9.0 release.

I think we are ready for an 0.8.6 release as-is from the python2 branch.

[kotfu]

I'd defer the preparse() and postparse() changes until a later release. As currently implemented the preparse() call will not receive all of the arguments of a multiline command.

[tleonhardt]

@kotfu I think I might revert the preparse behavior in this PR, but leave the deletion of postparse if that seems reasonable to you. And then you can fix preparse as part of the changes you are working on for #410.

[tleonhardt]

@kotfu Are you happy with the postparse() deletion present in this PR for now?

[kotfu]

Yup.