Testing the build executables of a bin crate.

'cargo' tests by default have no support for running tests on a build excecutable. This crate solves this.

There are some problems to overcome the cargo limitations.

1. Running cargo tests does not depend on the executables build, by default they are not compiled at test time.
2. There are no standard facilities to locate and execute them in a test.

BinTest solve these problems by running 'cargo build' at test time, parsing its output for identifying and locating the build executables. On request it creates a std::process::Command for the binary which can be used for any further testing.

The testcall crate uses this to build tests and assertions on top of the commands created by bintest.