Version 0.5.0

Version upgrades, including cross-building against Scala 2.11 and 2.10 (dropping 2.9 support), Maven Central hosting and full CI/CD.

• Discourse post

User-facing changes

• Bump crossScalaVersions to 2.10.6 and 2.11.8 (#102)
• Drop Scala 2.9 support (#105)

Testing and deployment

• Add CI/CD (#103)
• Add Bintray credentials to .travis.yml (#104)
• Update Open Exchange Rates credentials in .travis.yml (#109)
• Add Sonatype credentials to .travis.yml (#111)

Under the hood

• Bump to sbt 0.13.13 (#106)
• Remove scala-util dependency (#101)