DOC: Usage composition
DOC: Usage composition

 * Add 'nomenclature' paragraph, about "masking" and "discarding"
 * Swap TOC header to actual header, so it's bigger
 * Flesh out 'Binding TempVars Instances' section
 * Begin drafting the 'Inspecting Masked Variables within
   the Managed Context' section
   * Name is longer than I'd like, but not sure how to shorten
 * Few other text tweaks

bskinn/tempvars,bskinn/tempvars