JSHint: enforce more rules

[Indigo744]

I suggest we enforce more JSHint rules to bring Mapael up to current JS standard.
Also, it helps us catch more bug or typo (see the one at line 1470 that was not detected before).

The following JSHint rules are added:

    undef: true prohibits the use of explicitly undeclared variables
    eqeqeq: true enforce strict equality (=== and !==)
    forin: true requires all for in loops to filter object's items
    freeze : true prohibits overwriting prototypes of native objects
    nocomma : true prohibits the use of the comma operator
    nonew : true prohibits the use of constructor functions for side-effects

The following options are also added, only to remove some wrong warnings:

    esversion: 3 Legacy ECMAScript version (IE9 and below)
    browser: true use browser env
    devel: true allow console

The following JSHint rules are deleted (no longer relevant):

    laxcomma: true allow comma first coding style
    laxbreak: true allow unsafe line breaking

Also, all comments are removed from .jshintrc file as they are forbidden by JSON standard.
Instead, justification is in a Wiki page: https://github.com/neveldo/jQuery-Mapael/wiki/JSHint

[neveldo]

Hi @Indigo744 ,

Thanks for your PR. I think it will lead to a great improvement of the overall quality of the code.

I have just noticed what seems to be a little mistake in the CONTRIBUTING.md (I hope your adds to this file will motivate some more users to contribute !).

When fixed, everything should be ok to be merged !

[neveldo]

Maybe a small mistake here ?

it is however, it is very light. => it is however very light.

[Indigo744]

Fixed!

[Indigo744]

I've squashed and merged this PR (using option provided by GH), so there's not too much commit! I think we should try to do this as much as possible to reduce cluttering the commit tree :)

[neveldo]

Thanks for the fix and for the merge ! You juste made me discover this shortcut on github, I didn't know about it before ... I agree with you, it will allow the project history to be more clear and simple, I will try to think about it for the future merges !