Generate arrays of edge types, not vertex types.

This fixes issue #77.
Test that dfs throws an ArgumentError if g cyclic.

This fixes deprecation warnings in test/dfs.jl, but uncovers a bug :-(
Allow topological sorting with ExVertices.
Merge pull request #78 from pozorvlak/fix_tests

Fix some type errors and deprecation warnings
no need to specify the exception type in tests
use SVG travis logo
Update tests for new test_throws syntax
Merge pull request #80 from daviddelaat/fixargumenterrors

Update tests for new test_throws syntax