With this new environment option to gowork section, it is possible
to specify environment variables that will be set during the build,
more specifically when env.sh is sourced.

The implementation is a bit complex, so that the syntax is not strict
and whitespace are tolerated in the definition, ie. all these should be
understood:

    [gowork]
    environment =
      A=a
      B =b
      C= c
      D=d=d