Adds HTTP Basic Auth and Digest support

Currently the type providers do not support authorization.
This patch adds support for interpreting the userinfo part of the
provided URL, constructing HTTP Auth and Digest authorization
credentials (as SecureString), creating and passing them to
credentials cache and adding it to the web request also constructed.
The credentials are removed from the URL both before building the
credentials and the request. In presence of authorization credentials
the GetSample methods are disabled in order to divulging the credentials
to the generated assembly unbeknownst to the user.

Fixes #158
Update to documentation to mention userinfo authorization is supported

Currently the documentation does not mention that userinfo part is
supported to create authorization credentials. These updates add a
mention of it.
Adds HTTP Basic Auth and Digest support

Currently the type providers do not support authorization.
This patch adds support for interpreting the userinfo part of the
provided URL, constructing HTTP Auth and Digest authorization
credentials (as SecureString), creating and passing them to
credentials cache and adding it to the web request also constructed.
The credentials are removed from the URL both before building the
credentials and the request. In presence of authorization credentials
the GetSample methods are disabled in order to divulging the credentials
to the generated assembly unbeknownst to the user.

Fixes #158
URLs updated to use secured protocol

The authentication examples used http, not https. Fixed.
Fixes to embedding URLs with userinfo part to generated assemblies

Gustavo noticed a bug in checking if the URL is having userinfo part,
authorization credentials. This is done in order not to embed
authorization credentials to the generated assembly.
Fixes an issue where passwords are not transmitted as UTF-8 Base64 encoded strings, but rather encoded using the system codepage in use at the encoding moment. This could result in situation where non-[A-Za-z] passwords won't work on some locales. The fix is done by implementing a IAuthenticationModule. It looks like this is the approach to take to introduce a OAuth2 authentication too, with either implementing ICredential or inheriting from NetworkCredential appropriately.

Also, it seems like an approach where the user/programmer defines which credentials should be added to the cache should be preferred. It could be in that case the type provider interface should expose a method to add directly credentials either implementing ICredential or inheriting from NetworkCredential.

Also, code reorganized.

#fixes 158
Add - to the list of default missing values
Merge branch 'master' into 158-Http-Authentication