This patch is mostly a documentation cleanup for the

hostingsvcs.service module. All docstrings in the module are brought

into line with our conventions.
In addition, some internal API changes have been made:

The HostingServiceClient._build_request method was only ever used in

  one place so it has been removed and its definition been made inline.
The logic for adding HTTP basic auth headers to a request has moved

  into the URLRequest class. The external API for adding HTTP basic

  auth remains unchanged.
All default values that were mutable have been replaced with None.

  These methods now all check for None and generate the appropriate

  default value.
The HostingServiceClient._build_form_data has been made both a

  staticmethod (since it should never be looking at instance variables

  and public (since it is generally useful outside the class).
HostingServiceClient.build_form_data now generates a list of strings

  to append together, instead of repeatedly performing string addition.

  Also, multiline string literals are now used to generate the content

  instead of doing string concatenation. Interpolation has been changed

  to use dictionaries for clarity.

Built the docs.
Ran unit tests.