High level parser interface

[Sergei Lebedev]

Each YAML document corresponds to a single nakaz config, some conventions:

• top level keys must be named as Erlang applications;

• second level keys (sections) correspond to records, so for example:

  ---
  yawndb:   # application name
    flusher: 
      interval: 1000
  
    listener:
      interface: "0.0.0.0"

  implies that we should provide two records #flusher{} and #listener to nakaz:ensure call and only those records will be accessible via nakaz:use.

Note: turns out YAML doesn't support naming top level documents, oops.