Docs: make indentation to be consistent at 4 spaces
Docs: add more specific cases for function spaces rules

Closes #724
Better configuration, plugin support
Docs: add twitter and mailling list links
StringChecker: Fix failing test
StringChecker: Revert fix for failing test
Errors: Simplify rules debugging and prevent crashes in error reporters

- `add` method now throws on calls with invalid values
- set 0 as column in rules/disallow-mixed-spaces-and-tabs
- `add` throwing tests for add method

Fixes #743
Closes #744
requireTrailingComma: add option ignoreSingleLine

Closes gh-737
Fixes #626
StringChecker: unsupported rules shown as style errors and not thrown exceptions

Closes gh-710
Fixes #334
disallowMultipleVarDecl: add exception for undefined variable declarations

Closes gh-749
Fixes #451
Update unit-coverage to 3.2.0
Readme: Add Plugins section

Closes gh-761
Fixes #760
Docs: Added clarification of tokens in disallowSpacesInConditionalExpression

Closes gh-763
Docs: Typo fix

Closes gh-766
New Rule: disallowOperatorBeforeLineBreak

Fixes #511
Closes gh-754
requireCapitalizedComments: Better support for multi-line comments

Closes gh-769
Fixes #767
Errors: Support a filter to control which errors are reported

Closes gh-728
Fixes #335
Iterate over "export" statement of ES6

Fixes gh-753
Preset: Grunt

Fixes #742
Error Filter: Handle null value

Closes gh-776