Compilation error `Unknown key “path”` was present when using Solidity 0.5.x. This PR removes the path property from the compilation sources as it is not needed.
Changes include:
- Before compilation, for each contract file being compiled, recursively remaps the contract's imports.
- Allowed directories for compilation updated based on the remapped import paths for the contract file.
- Support for code coverage flag.
- Fix for unhandled promise rejection when attempting to use an insufficient version of solc.
