Also add better comments

Turns out we were nixing the default browser spacing for bullets and
numbers, so this reverts that and instead just twerks the top/bottom
`margin`.

* Update docs to include table of grid levels and behaviors
* Change from .col-md to .col-sm to match existing size variables we use elsewhere
* Keep .col-lg as-is though for simplicity as we won't likely add a fourth level of the grid
* Combine responsive .container breakpoints with grid breakpoints in grid.less
* Other misc docs updates

- Removed mixins for generating grid classes
- Thus, we manually declare every grid class, from 1-11 (12th unit is
excluded as that's the same as no grid columns)
- No more need for `.col` base class (yay!)
- Negative indent the rows at tablets and above once again (ugh, still
working through this part)
- Add support for `.col-md` for tablet-specific grid columns
- Still need to figure out offsets, pushes, and pulls on other
devices—right now only available on desktop

* Add start and end support to the horizontal gradient as well
* Change all variables from camelCase to use-dashes
* Better comments in the gradients mixins area
* Update current uses of gradients in dropdowns and carousel to specify only two values by direct assignment of variables

* No more negative side margins
* However, keep the negative margin for nested rows

* No more children selectors to set all links in alerts as a special color because buttons and more wrongly inherited color
* Adds .alert-link for easy styling in any alert

* changed .row-label to .control-label as used elsewhere already
* changed .formFieldState mixin to .form-field-validation

* Update docs language
* Enforce display: block; on all utilities for now
* Fix up docs CSS for the tests

change dropdown strategy to use an overlay - fixes mobile click anywhere + allows for firefox middle click

* New padding approach with separate horizontal and vertical padding
variables
* Improved sizing in large and small buttons and form controls
* Dropped the `.btn-mini` (since we have no `.input-mini` to match, and
holy fuck those were small buttons)
* Dropped the `.pagination-mini` as well because once again, to hell
with such small components
* Changed `@line-height-headings` to `@headings-line-height`
* Removed the `@headings-font-family` because it was honestly kind of
useless

* Remove border-radii on top of tab dropdown menus
* Remove the .dropdown and .dropup styles and instead place  on all
* Use  on dropdown carets intead of separately applying margin with a top alignment
* Some other misc cleanup

* Use 1.428 for line-height instead of 1.5
* Use  function for full pixel values instead of decimals