Add max-file-line-count rule

[DanPurdy]

Adds the rule max-file-line-count to enforce the length of a file

If a file exceeds the default / user specified line count the following message will be provided:
This file has 301 lines, which exceeds the maximum of 300 lines allowed.

closes #841

<DCO 1.1 Signed-off-by: Dan Purdy dan@danpurdy.co.uk>

[coveralls]

Coverage increased (+0.02%) to 97.268% when pulling 8bc0aa7 on DanPurdy:feature/max-file-line-count into 54c25a9 on sasstools:develop.

[bgriffith]

Typo - file's

[bgriffith]

This could be simplified as all we need is the end.line of the stylesheet node (ast), which will always be ast.end.line

[bgriffith]

...  
  'detect': function (ast, parser) {
    var result = [];

    if (ast.end.line > parser.options.length) {
      result = helpers.addUnique(result, {
        'ruleId': parser.rule.name,
        'line': ast.end.line,
        'column': 0,
        'message': 'This file has ' + ast.end.line + ' lines, which exceeds the maximum of ' + parser.options.length + ' lines allowed.',
        'severity': parser.severity
      });
    }

    return result;
  }
...

[coveralls]

Coverage increased (+0.007%) to 97.57% when pulling 8167ede on DanPurdy:feature/max-file-line-count into 1a1f695 on sasstools:develop.

[coveralls]

Coverage increased (+0.007%) to 97.579% when pulling bb321ce on DanPurdy:feature/max-file-line-count into d2c4ce4 on sasstools:develop.