Corrected memory leak

All type providers were implementing
DisposableTypeProviderForNamespaces, which re-implemented IDisposable,
effectively hiding the base class Dispose() method call.  This causes a
leak as the AppDomain AssemblyResolve handler was never unsubscribed.
Merge pull request #641 from ReedCopsey/master

Corrected memory leak
Update RELEASE_NOTES.md
Accept more MIME types in HTTP requests

Currently when reading text from a URL, the MIME type is set to the
specific format being requested, e.g. application/xml for XML. This
will cause the request to fail with HTTP error 406 if the resource
has a different MIME type, such as text/plain or application/atom+xml.
This commit modifies it to prefer specific types, followed by */* so
that any MIME type is accepted.
Merge pull request #648 from lasandell/AcceptAnyContentType

Accept any MIME type in HTTP requests
Update RELEASE_NOTES.md
Update .travis.yml
EscapeUriString changed to EscapeDataString so ampersands can be used as arguments

Used EscapeDataString to encode components of the URI rather than
EscapeUriString.  Using EscapeUriString does not escape query parameters
containing ampersands correctly.
Bug: Http - writeBody called before call to customizeHttpRequest
Merge pull request #655 from nkw/master

Bug: Http - writeBody called before call to customizeHttpRequest
Update RELEASE_NOTES.md
Merge pull request #654 from ACassells/master

EscapeUriString changed to EscapeDataString
Update RELEASE_NOTES.md
Merge branch 'master' into HtmlTypeProvider