Update tests to reflect GitHub's new path to raw content

The dynamic sidebar tests use macros, which are located on github via
raw URLs. When they changed their path, it didn't cause any failures
while also slowing down the tests (see #369).

This commit updates the tests to use the new paths and also added a
check to verify that macro content was actually loaded. Both should
cause a more recognizable failure if github makes similar edits.

The impact is that all the guides need to be updated to reflect the new
paths.
Ignore DynamicSidebarTests

Related to #369 and #379, this commit comments out DynamicSidebarTests
until we're able to figure out and solve whatever problem is causing
them to execute so slowly (on the order of 30 seconds--unacceptable for
any unit test).
Modify and merge pull request #379 from gregturn/github-raw-content-moves

Changes from original pull request:

 - Added commit ignoring DynamicSidebarTests, as they remain extremely
   slow even after the changes in this PR.

 - Reformatted commit comments for style.

Resolves #379