Release 1.6.0

```
Aki Saarinen (1):
      Merge pull request #144 from jvirtanen/features/bats-souptcpfile

Bob the Builder (1):
      Stirling 1.5.1-SNAPSHOT

Jussi Virtanen (35):
      Extract BATS SoupTCP file support
      Change BATS PITCH 1.12.0 specific message parser into object
      Rename BATS PITCH 1.12.0 SoupTCP file test
      Clean up imports in BATS PITCH 1.12.0
      Unseal BATS PITCH 1.12.0 message type
      Extract BATS PITCH 1.12.0 specific Commons trait
      Clean up BATS PITCH 1.12.0 message parser
      Refactor BATS PITCH 1.12.0 message parser
      Add BATS PITCH 1.12.2 support
      Use BATS PITCH 1.12.2 as baseline
      Add BATS PITCH 1.12.0 specific constants
      Upgrade to Silvertip 0.4.1
      Add license header to MBT Quote API source files
      Remove superfluous import from MbtMessage
      Remove superfluous imports in MbtMessageSpec
      Remove superfluous semicolon from MbtQuoteServerTickCondition
      Add some whitespace to MBT Quote API
      Add some more whitespace to MBT Quote API
      Remove 'MbtMessage#isMarketDataMessage'
      Add return types to MBT Quote API
      Simplify MBT Quote API parser
      Align enumerations with types in MBT Quote API
      Use option for getters in MBT Quote API
      Clean up setters in MBT Quote API
      Remove 'MbtMessage#hasValue'
      Make 'MbtMessage#get' private
      Remove 'MbtMessage#merge'
      Use ASCII encoding in MBT Quote API
      Remove timestamp handling from MBT Quote API
      Add 'MbtMessage.Fields'
      Convert MbtMessage into sealed trait
      Rename 'MbtMessage#set' to 'updated'
      Align names to specification in MBT Quote API
      Align constants to specification in MBT Quote API
      Add MBT Quote API session support

Pekka Enberg (4):
      Merge pull request #143 from valotrading/releases/1.5.0
      Merge pull request #146 from jvirtanen/features/silvertip-0-4-1
      Merge pull request #147 from jvirtanen/features/mbt-quoteapi-1-7
      Merge pull request #145 from jvirtanen/features/bats-pitch1122
```