v1.0.0-rc4

Fourth release candidate https://github.com/tarkhov/postboot/milestone/2

1. Improved flex utilities.
2. New svg utilities for easier svg images customizing.
3. Most of components sizes become responsive: borders, buttons, breadcrumbs, cards, dropdowns, form inputs, grid rows, navs, nabars, pagination, progress.
4. Added new grid columns named .col-2-5 with 20% width for 5 column rows.
5. New sizing utilities for width and height combined, like .s-100.
6. Classes for button active and hover color state, like .btn-hover-primary and .btn-active-primary.
7. Distributions archive contains 3 versions of PostBoot library: default (full) 459KB, light (without colors) 160KB and grid only 15KB.