(PE-3366) Add link to testutils docs

Add a link to the testutils docs in the README.
(TK-47) Modify endpoint data structure

Modify the list of endpoints to be a map. Now, since an
endpoint can have multiple handlers registered on it,
each key in the map is an endpoint, with its value being a
vector of all the handlers registered at that endpoint.
(TK-54) Fix multiple default servers error message

Fix multiple default servers error message to be something
readable.
Merge pull request #79 from fpringvaldsen/PE-3366-testutils-link

(PE-3366) Add link to testutils docs
Merge pull request #81 from fpringvaldsen/TK-54-default-server-error

(TK-54) Fix multiple default servers error message
Merge pull request #80 from fpringvaldsen/TK-47

(TK-47) Modify endpoint data structure