Add "version" command

for parity with foreman.
honcho export --help: List format choices

Before:

    $ honcho export --help
    ...
      FORMAT                format in which to export

After:

    $ honcho export --help
      FORMAT                format to export to; one of upstart, supervisord
export: Reverse order of FORMAT and LOCATION args

to match foreman

    $ foreman help export | head -n 2
    Usage:
      foreman export FORMAT LOCATION

Fixes: GH-91
export: Don't require log directory to exist

`-l`/`--log` is the directory to place process logs in, so you should
only need this directory at runtime. The log directory shouldn't be
required to exist at export-time, because you might just export the
Procfile to a supervisord config and then use that exported config to
run processes on another box altogether.

[marca@marca-mac2 export_test]$ ls -l
total 8
-rw-r--r--+ 1 marca  staff  23 Nov 26 08:15 Procfile
[marca@marca-mac2 export_test]$ honcho export . supervisord
[marca@marca-mac2 export_test]$ ls -l
total 16
-rw-r--r--+ 1 marca  staff   23 Nov 26 08:15 Procfile
-rw-r--r--+ 1 marca  staff  354 Nov 26 11:15 export_test.conf

Fixes: GH-90
supervisord template: \n at end; not at beginning

It's a UNIX convention that text files should always end with a newline.
One of the best reasons for this is that it makes possible to do `cat
file1.txt file2.txt > combined.txt` and have the result make sense. For
more info:

http://stackoverflow.com/questions/729692/why-should-files-end-with-a-newline

I also modified the template slightly so it doesn't generate a blank
line at the beginning of the file. I don't think it does any harm, but I
think it looks slightly better without it.
Add logging to test_supervisord_concurrency

This turned out to be very useful when debugging test failures I was
getting while working on PR #96.

nosetests has built-in support for capturing log output and printing it
(pytest can also do this if you `pip install pytest-capturelog`).
Merge pull request #94 from msabramo/export_no_require_log_dir

export: Don't require log directory to exist
Merge pull request #97 from msabramo/test_export_supervisord__log_generated_contents

Add logging to test_supervisord_concurrency
Merge pull request #92 from msabramo/export_reverse_argument_order

export: Reverse order of FORMAT and LOCATION args
Merge pull request #89 from msabramo/export_help_list_format_choices

honcho export --help: List format choices
Merge pull request #96 from msabramo/supervisord_template_newline_at_end_not_at_beginning

supervisord template: \n at end; not at beginning
Merge pull request #87 from msabramo/add_version_command

Add "version" command
export: Add help string for -p/--port option
Test python 3.4 with tox and Travis CI
Fix broken tox docs target

This change prevents me from getting the following errors:

    $ tox -e docs
    GLOB sdist-make: /Users/marca/dev/git-repos/honcho/setup.py
    docs inst-nodeps: /Users/marca/dev/git-repos/honcho/.tox/dist/honcho-0.5.0.zip
    docs runtests: PYTHONHASHSEED='3860990299'
    docs runtests: commands[0] | sphinx-build -W -b html -d /Users/marca/dev/git-repos/honcho/.tox/docs/tmp/doctrees .  /Users/marca/dev/git-repos/honcho/.tox/docs/tmp/html
    Running Sphinx v1.3b1
    making output directory...

    Exception occurred:
      File "conf.py", line 51, in <module>
        from ..honcho import __version__
    KeyError: "'__name__' not in globals"
    The full traceback has been saved in /var/folders/gw/w0clrs515zx9x_55zgtpv4mm0000gp/T/sphinx-err-bu6qxnzx.log, if you want to report the issue to the developers.
    Please also report this if it was a user error, so that a better error message can be provided next time.
    A bug report can be filed in the tracker at <https://bitbucket.org/birkenfeld/sphinx/issues/>. Thanks!
    ERROR: InvocationError: '/Users/marca/dev/git-repos/honcho/.tox/docs/bin/sphinx-build -W -b html -d /Users/marca/dev/git-repos/honcho/.tox/docs/tmp/doctrees .  /Users/marca/dev/git-repos/honcho/.tox/docs/tmp/html'

and:

    Warning, treated as error:
    /Users/marca/dev/git-repos/honcho/doc/api.rst:9: WARNING: autodoc: failed to import module 'honcho.procfile'; the following exception was raised:
    Traceback (most recent call last):
      File "/Users/marca/dev/git-repos/honcho/.tox/docs/lib/python3.4/site-packages/sphinx/ext/autodoc.py", line 378, in import_object
        __import__(self.modname)
    ImportError: No module named 'honcho.procfile'
Tweak docs for adding export format support

* Reword English a bit
* Syntax highlighting of Python code
* Enable links to the classes and methods involved
Merge pull request #108 from msabramo/improve_docs_on_adding_export_format_support

Tweak docs for adding export format support
Merge pull request #104 from msabramo/fix_tox_docs_target

Fix broken tox docs target
Merge pull request #100 from msabramo/test_python3.4

Test python 3.4 with tox and Travis CI
Merge pull request #99 from msabramo/export_port_add_help_string

export: Add help string for -p/--port option