Rewrite to attend all initial recommendations

Closes #1, #2, #3, #4, #5, #6 and #7.
Add package documentation and README
Changes after PR suggestions

Naming changes:

  * JSON tags changed to camel casing.
  * Time attributes abbreviated as "Tm" changed to full "Time".
  * Full "journal" concept changed to "history" (vars, docs, URL).

Other changes:
  * CancelErr changed to string type.
  * Added option to forbid cancellation.
  * README.md rewritten with only an overview.
Add functions to set/delete attributes
Merge pull request #11 from VividCortex/rewrite

Rewrite to attend all initial recommendations