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 example sections to include basic, mobile-desktop, and mobile-tablet-desktop implementations
* Add more examples to the grid example page
* Red columns instead of gray for more Bootstrapy aesthetic

* 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

add show/shown hide/hidden events to dropdown + update dropdown links for testing + catch a few missed namespace things

I reworked the customizer to match the new docs layout and include all
newly added variables, etc.
Would be glad to keep an eye on Customize and update it as v3 changes.
Help blocks in my new version need some more work, too, so this is just
a basis.

* 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