Implemented Test:
   - issue two currencies USD and BTC via @currency contract
   - create EXC exchange between USD and BTC
   - buy BTC with USD and then sell proceeds back for BTC
   - verify only error is rounding error in favor of exchange

Added missing Float compilier intrensics
Added flaot64 types to WAVM api
Added print functions for asset in WASM contracts

Fix binary WASM detection in eosioc

Fix using a binary wasm for set constract. This check got goofed up. Fixes issue reported in #1579

Validate JSON format of contract abi files.

update libc to new version and fix CMake (compile math library)

Txn test dependencies fix

From a script by @joneric.

quad precision floating point builtins added

Fix Docker builds

switch to next version of our libc and libc++ (with floating point)

Fix GitHub issue #1591 and add test case related to the bug

 Be proper UNIX citizens in expected directory hierarchy.

Add support for Linux Mint (as an ubuntu variant) to the build scripts

Changes in order to get rid of contract warnings

Fix/add back cmake defaults