Specify bash shell when validating sudo snippet

Since we are using bash specific features and sometimes you can end up getting /bin/sh - see https://github.com/saltstack-formulas/users-formula/pull/30#issuecomment-44224106

Overwrite a sudoer file rather than append to fix #21

Do not echo Public/Private keys to stdout when running the state

Ensure that we are sudo includes /etc/sudoers.d

It doesn't by default everywhere - without this the sudo_rules option won't work

Validate user sudo rules before applying them

Add Password if the state supports it.

corrected url for formulaes...

New format of handling user.absent, supporting additional parameters

Fix incorrect sudo_rules example

Add home to pillar.example

Fix pubkey privkey typo

Fixes #22

Add absent_groups pillar to remove groups.

Updated structure of readme, bumped License to 2014.

Check for sudo_rules before text.append state.

Since ebe5198f, if a user's pillar dict didn't contain sudo_rules, a broken
file.append state would be rendered (since some text is required). With
this patch, the file is still created/managed by the previous state, but
will be empty by default if created fresh. This seems a more sensible
default than assuming a default sudoer policy.

Further, since the first word on each rule line should be the user's
name, that is now assumed.

Changed 'contents' to 'contents_pillar' to correctly parse newlines for private/public SSH keys.

Fix ssh_auth.names in example pillar

Change .ssh directory permissions to 700

Add and support ssh_key_type attribute to allow for dsa ssh key pairs

Cleaned up Documentation and User state

if you set an alternate prime_group this would break, replaced {{ name
}} with {{ user_group }}

had the prime group and ssh keys values as another dict. fixed.

Changed Private keys to have content within pillar rather than the salt
file repository.

Changes sudoers entry to get values from pillar rather than assuming
all sudo users want root.

Revising example pillar to add a minimal required values and a full
list of available values

SLS no longer fails for multiple groups

possibility to define alternate user`s prime group

Fix Undefined jinja variable error with Salt 0.17.1

Ran into an error with Salt version 0.17.1:
Rendering SLS users failed, render error: Undefined jinja variable; line 32

After finding https://github.com/saltstack/salt/issues/8245, and working on
line 32, I surmised that line 28 might be the actual cause of the issue.

I just added a quick check to see if uid exists in user, just as the user uid
line does.

better sudoers support & default gid