update docs with a better API section
Prettier / terser size() logic.

Characters cost money.
Make width non-required in ellipsis() mixin.
[touchup] Strip readme whitespace.
Make pos() less hacky.

By using loops and variable arguments.
Allow bypass of property in pos() with 'false'.
Add "fill" argument to pos() mixin.

Passing `fill` as an argument will set the top, right, bottom, and left
properties to 0.

The 0 for an individual property can be overridden by giving it a value.

pos(absolute, fill)

position: absolute
top:      0
right:    0
bottom:   0
left:     0

---

pos(fill, 50px)

top:    50px
right:  0
bottom: 0
left:   0
Bump version, add changelog.