Support for \usepath and some cleanup

Squashed commit of the following:

commit 88ff39385acfa7976476fb6dcd0a949d18bd6249
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Wed Jun 20 16:13:03 2012 -0400

    Bump version number

commit 4b8801e5c91996efda15bdf0a213dac7fcc4a744
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Wed Jun 20 16:01:34 2012 -0400

    Honor \usepath in MkII as well

commit 1716733ff29727ebe8d89b953501ed834a4188ab
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Wed Jun 20 15:41:40 2012 -0400

    Honor \usepath to find files

commit 6384ed49a62448ed24f397222f59f890433c5348
Merge: 2c2631c c8dbfb6
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Sat Jun 16 17:09:20 2012 -0400

    Minor changes so that MkII and MkIV matches

commit 2c2631c237eeade324fed57a14f17a5d624f19c6
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Sat Jun 16 00:47:39 2012 -0400

    Bump version number

commit 3b2040c318a695eff5cc78a1feb38dcdb0f90b35
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Fri Jun 15 23:01:59 2012 -0400

    Documented interiting settings

commit 2170f6cfb35029881afde3639f7a99e4ee1e7b25
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Sat Jun 16 00:43:35 2012 -0400

    Ensure that inheritence works in Mkii

commit 3c5183f0818321c98ed4b24db94273a49983ca8b
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Fri Jun 15 23:24:40 2012 -0400

    Refactoring:

    Anything that removes \expandafter from code is good!

commit f3d69ad814e18bff37a747e8af124cd5d31d25d4
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Fri Jun 15 22:39:54 2012 -0400

    Only define a new counter if it does not exist.

    When using pandoc to generate context file, it is useful to redefine
    the `typing` environment as a vimtyping environment using

        \definevimtyping[typing][...]

        markdown code

        \definevimtyping[typing][...]

        more markdown code

    Currently, \definevimtyping effectively resets the counter, the first temp file
    is overwritten by the second, and we only get one code listing in the output.
    The current change fixes this bug.

commit 29bc808007eee100c3dfe1018ff44f9715a9b413
Author: Aditya Mahajan <adityam@umich.edu>
Date:   Sun Jun 10 13:56:29 2012 -0400

    Give an error message if the file is not writable

    Otherwise t-vim fails silently if non-existing directory is specified as output
    directory.
Added `margin` option to vim module
Added OSM webfilter
Merge pull request #9 from reviczky/master

Adding OSM (OpenStreetMap) webfilter
Support for write=no
Support for left and right
Bugfixes

- `filtersetups` now works with `process<filter>file`
- vim module works with Mkii again
Update README.md

typo in *changes in between successive runes*?
Merge pull request #13 from ousia/patch-1

Update README.md