Plug with Travis CI service

Following customizations are required to get ~stable builds on travis
cloud workers:

- Avoid test timeouts with akka.test.timefactor=1.5
- Avoid memory problems with smaller thread stack size (Xss2m)
- Avoid non-deterministic timing/perf issues by serializing the tests
  (set concurrentRestrictions in Global += Tags.limit(Tags.Test, 1))
Merge pull request #233 from gildegoma/add-travis-ci

Integrate with Travis CI
http: major refactoring for cleanliness and perf, introduce Rendering infrastructure
can: upgrade to new spray-http and rendering infrastructure
diverse: upgrade to new spray-http
fix comment typo
http: add specs for http model classes serializability
http: also try deserializing in HttpModelSerializabilitySpec
http: more tests for http model header value instances
http: establish serializability for complete HTTP model, closes #278
can: add logging of warnings for explicitly set request- and response headers that are ignored by the HTTP message renderer, closes #221
util: fix #207 by renaming `spray.util.pimpAny` and `spray.util.pimpString`
diverse: prevent NPEs during exception handling using `e.getMessage`
http: protect creation of "special-status" headers with dedicated implicit requirement
move SetRequestTimeout and SetTimeoutTimeout to spray-http and use additionally for srpay-servlet
sbt: upgrade to sbt-boilerplate 0.5.1
routing: fix compile-time problem in HListDeserializer
can: improve PipelineLimiter implementation
Merge branch 't3hnar-master'
servlet: small fix in Servlet30ConnectorServlet