Rewrites organization

- Create lib/rewrites.php and move everything from lib/htaccess.php
except the H5BP htaccess functionality into it

- In the config, change add_theme_support('rewrite-urls') to
add_theme_support('rewrites')

- Remove the Apache/LightSpeed HTTPD check for rewrites

- Update docs with better Nginx rewrite rules

doc/usage.md

@@ -42,6 +42,7 @@ A basic Roots theme initially looks like this:
 │   ├── htaccess.php
 │   ├── init.php
 │   ├── nav.php
+│   ├── rewrites.php
 │   ├── scripts.php
 │   ├── sidebar.php
 │   ├── utils.php