Add a marshaller for Try objects.
Modify spray-can to allow dynamic User-Agent header

- Client is allowed to set only when spray.can.client.user-agent-header setting is blank
Merge pull request #184 from dpratt/try-marshaller

httpx: add default marshaller for Try[T]
Merge pull request #194 from chaptastic/ua-restriction

can: allow for dynamic specification of User-Agent header, closes #193
can: make ParserSettings public
http: relax syntax requirements for OAuth2 Bearer token parsing
client: fix connection close not registered by HttpHostConnector
routing: add `options` directive for matching OPTIONS requests
introduce lift json support in httpx for 1.1