Add more information about running tests, add syntax highlighting

There was no information in the README about how to handle multiple
tests for a given extractor. This commit adds an explanation of how this
is handled.

It also adds some syntax highlighting.
Added an IE for Dump.com
Added test for dump.com
[metacafe] Add support for movieclips videos (Fixes #3555)
Merge remote-tracking branch 'yasoob/master'
[dump] Modernize (#3565)
[aparat] modernize
Merge remote-tracking branch 'terminalmage/readme'
[README] brevity is the soul of wit

These instructions are overly long as it is. Leave out the _TESTS example; most developers will not need it in their first IE.