docs(guides): several fixes (links, typos, syntax, line lengths)

[gkalpak]

I started out fixing line-length to comply to the max. 100 chars per line rule (as discussed here), but this turned out to be a more generic error fixing:

• Fixes wrong or broken links
• Fixed typos/punctuation/syntactic errors
• Rephrazed at a couple of places, where the wording sounded unclear or confusing
• Wrapped lines at 100 characters

_{The diff may seem a little weird due to the line-wrapping.}

I have re-read all the modified documents and tried all the links (and everything seems fine), but a 2nd pair of eyes is always irreplaceable 😃

[googlebot]

CLAs look good, thanks!

[gkalpak]

A couple more notes/issues:

1. In PULL_REQUESTS.md:
   • It is mentioned that commit messages should "pass our commit message presubmit hook validate-commit-msg.js". But there is no such script.
     Should we bring it over from AngularJS or remove the corresponginfg line from PULL_REQUESTS.md ?
2. In CODING.md:
   • It is mentioned that the SCSS file for each component should be named <component>.scss. A few components I checked though, seemed to name it _<component>.scss. I wonder what's the reason (and if we need to correct the docs).
   • There a 2 links pointing to AngularJS resources, namely:
     https://github.com/angular/angular.js/wiki/Writing-AngularJS-Documentation and
     https://docs.angularjs.org/guide/unit-testing
     Both seem relevant, but I thought I'd just ask if this is OK.
3. In COTRIBUTING.md:
   • This is pretty minor, but I got to mention it anyway: The 2 issues given as examples of well formatted issues (Bottom sheet and sidenav overlapping (v2) #629, Implement BottomSheet component #277) are pretty OK, but (imo) not "examplary" (e.g. they provide none or very little of the requested info). _{(I don't claim mine are any better by any means.)}

[gkalpak]

It would be great if someone could take a look at this and merge it some time "soon-ish". It's purely docs.
There are a lot of files/lines affected and having to rebase on master is not painless.

[ThomasBurleson]

@gkalpak - I will review later this morning.

[ThomasBurleson]

In the future, please add linebreaks as it makes side-by-side git reviews very difficult.

[gkalpak]

The reason side-by-side review is difficult is because I have linebreaks, but the old version didn't. Basically, the original intent of this PR was to apply the max. 100 chars/line rule the docs, because the long lines made reviews difficult. So, hopefully, future reviews will be much easier :)

[ThomasBurleson]

Will merge now. Thx @gkalpak

[gkalpak]

@ThomasBurleson: Many thx for reviewing (and merging) - I know it was tedious.

BTW, you might want to take a look at #837 (comment).
(For (1), I believe some action is required. For (2), just a confirmation that nothing needs to be changed. (3), you can just ignore.)

[ThomasBurleson]

@gkalpak - Will do. Thx for the alert.

[ThomasBurleson]

@gkalpak re > your comments above "A couple more notes/issues"

(1) Fixed
(2) Good point... Fixed in SHA 629b753
(3) Those examples are reasonable because they present an issue with a snapshot and reference to a the spec. Other reasonable examples would be snapshots with formatted code snippets, etc. You are welcome to suggest others that you feel are more appropriate.