Reformatted --diff-filter git argument

This makes the command compatible with older versions of git.

Fixed regex matching for django test file names

Add encoding pragma hook.  Resolves pre-commit/pre-commit#15

Show names of files containing aws credentials

Update description about autopep8.  Closes #83

Sort requirements.txt case-insensitively

Add a hook to verify python ast.

detect_private_key: print *filenames*, not the key

Add .pp (Puppet manifest) to file extensions lists

AWS credential checking

add tests, test sample files and minor refactor of exit codes in actual hook in order to facilitate testing

ditch checkign access_key (don't consider these a secret)
don't check line by line, check the whole file in bulk instead

Allow arbitrary binary to pass the private key hook check.  Resolves #64

Add new hook pretty-format-json

This new hook allows to standardize one's JSON files (sorted key/4
spaces indent).
By default it just fails if any file is not complying with the standard,
but you can also pass the arg `--autofix` and the hook will
pretty-format the file itself.

Good in use combined with the `check-json` hook.

add aws credential checking ONLY FOR YOUR OWN credentials if they're set in a configurable credentials file (AWS CLI tools' native format)

Implement Markdown trailing space line break preservation

Markdown uses two or more trailing spaces on a line to indicate a forced
line break `<br/>` - these will be preserved for files with a markdown
extension (default = `.md` or `.markdown`).

Add `--markdown-linebreak-ext=X,Y` to add extensions (`*` matches any),
and `--no-markdown-linebreak-ext` to disable this feature.

If you want to set specific extension `foo` only (and not md/markdown),
use `--no-markdown-linebreak-ext --markdown-linebreak-ext=foo`

Tries to prevent --markdown-linebreak-ext from eating filenames as if they were
extensions by rejecting any with '.' or '/' (or even Windows-style '\' or ':')

Update README.md to include information on these arguments as well as
arguments added to other hooks

Add extensive tests using pytest.mark.parametrize

test that `txt` file is not considered as 'txt' extension
test that `.txt` file is not considered as 'txt' extension

The latter is the (correct) behavior of os.path.splitext(), and an example
of why it is better to use the libraries than to mangle strings yourself.