Docs improvements notes

[ned14]

• "AFIO single page cheat sheet for the very impatient" -> "Getting

  started". Move table to the top of the page, replace the "Related types"
  column with "Boost.Filesystem sync alternative", replace numbers with
  checks/+/-.
  * Move the "Example mini-programs written using AFIO" chapter right after
  the "Getting started", rename chapter into "Tutorial", refactor second
  example to not use batch operations and to use only free standing
  functions. Third and fourth examples must be greatly simplified and
  probably split into smaller examples.
  * Move the content of "Step by step workshop building an AFIO-based
  key-value store" into the "Tutorial" after the previous examples, rename it
  into "Key-value store walkthrough", simplify and make shorter if possible
  * "Compilation" section must be somewhere around "Getting started"
  * Other docs must be after the "Getting Started," "Tutorial" and
  "Compilation"
  * "Reference" section must be refactored. All the overloads must be
  probably described and showed on a single page (all the overloads,
  including those that explicitly accept dispatcher)
  * Shorten and simplify the examples wherever possible.