Minor: Updated LESS comments

• Switched to using `//` and `///` comment syntaxes, since it's easier to type, modify, and read.
Parent/child screenheight % generation LESS

In mixins.less:
• New `screenheight()` macro calculates the height percentage of a child class relative to its parent.
• New `generate-screenheights()` macro generates rules for each of the percentage values in the passed-in `screenheights` arrays, and child rules (`screenheight-100 { … > screenheight-50 {} }`) for each of the possible child screenheights (those at or bellow the parent's percentage).
	» Yeah… Wow.  The fact that this is even possible is amazing.
	» Safely handles normalization of array values to class-friendly numbers or percentages where needed.
	» Should be able to expand to any number of percentage options, and to do a third level if wanted.
	• Uses the fantastic `for.less` mixin plugin, added from https://github.com/seven-phases-max/less.curious/blob/master/src/for.less

In main.less:
• Added `html, body { height: 100%; }` necessary for full-height CSS to work.
• Added a `.generate-screenheights()` call for heights 50%, 100%, 150%, 200%, 300%, and 400%.
	» And it all works!  Srsly'mazing.
Added `screenheight-*` classes to each <section>/.container

• Added `screenheight-*` to each of index.html's Bootstrap containers.
	• And added to each <section> with a height totaling all of its child containers.
• Also added debug `background-color`s to each of the <section>s.