Expose statement-component validation functions

[ZackPierce]

As raised in #2 , there may be utility in exposing validation capabilities for xAPI statment component objects (e.g. verbs, actors, etc) independent of an entire statement.

My present thinking is a two-parameter function returning a report object.

• target param that's either a JSON-string or an object

• optional version param that is a Semantic Version 1.0 compliant string, or an object formulated like

  {
   major:1, 
   minor:0, 
   patch:0, 
   preRelease:null
  }

  Defaulting to "1.0.0"

• returns a report object that includes:

  • validated version string
  • input target param post-deserialization as instance
  • errors array. The trace property value conventions in errors may also merit revisiting to remove prefix-cruft.

Possible targets:

• Verb
• Actor
• Agent
• Group
• Context
• Object
• Activity
• Result