RFC: Allow general vertex types (fixes #105)

* As noted in #105, before this PR, vertices really only
  could be Integers (including Char), KeyVertex, or ExVertex,
  mostly because of explicit calls to vertex_index(v).
* This PR changes most calls of vertex_index(v) to
  vertex_index(v,g), and makes sure to only call
  vertex_index(v) for types that it is defined for
* Also provides a slow fallback vertex_index(v,g) for
  non-provided vertex types when the graph's vertex list
  is an AbstractArray.
* Tests also included
Remove @assertions during vertex, edge creation

* These were restricted so that the number and element location
  were identical
Merge pull request #106 from JuliaLang/kms/general_vertex_types

RFC: Allow general vertex types (fixes #105)
Extracted the non general property  extractors from the library, put them as examples in test.  Still need to try documentation.
removed non general inspectors from common.jl
Merge branch 'master' into fix_a_star
brought documentation up to date