Add max-line-length rule

[DanPurdy]

Adds the max-line-length rule by default it is disabled in the config.
It specifies a default value of 80 characters long.
If a line breaches the default or user set limit it will warn with the message:
line 1 exceeds the maximum line length of 80

closes #833

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

[coveralls]

Coverage increased (+0.01%) to 97.264% when pulling ecdcc98 on DanPurdy:feature/max-line-length into 54c25a9 on sasstools:develop.

[coveralls]

Coverage increased (+0.01%) to 97.264% when pulling 9836960 on DanPurdy:feature/max-line-length into 54c25a9 on sasstools:develop.

[DanPurdy]

@bgriffith this looks to fall victim to that same CRLF .sass issue we were looking at earlier. Should i patch in here or wait for the gonzales release with that particular issue fixed?

[coveralls]

Coverage increased (+0.01%) to 97.539% when pulling 4bf2237 on DanPurdy:feature/max-line-length into a66c707 on sasstools:develop.

[bgriffith]

@DanPurdy Hey - is this good to go now on the CRLF front?

[DanPurdy]

Yup if the tests are passing.

[coveralls]

Coverage increased (+0.01%) to 97.541% when pulling 5123ca5 on DanPurdy:feature/max-line-length into 8a3f293 on sasstools:develop.