Put the mozlog.sructured standard logging adapter in a seperate file.

It turns out that this is needed to use multiprocessing on Windows,
because the inner-class design doesn't pickle.

--HG--
extra : rebase_source : 27d5125ccf9e0edd3fe466b2f7b2c5f6790715e2
Bug 945222 - Make web-platform-tests work on windows

--HG--
extra : rebase_source : b37bc239a5b16b266b22a986542ee356444b428c
Bug 914563 - Split mach into two so that "import mach" in the source directory works.

This is needed so that multiprocessing works in mach scripts on Windows.
Because Windows doesn't have fork, multiprocessing tries to import the
initial script (i.e. mach) on Windows. Doing this requires a mach.py
file to exist. However it is important that this mach.py not end up on
the system path in mach_bootstrap.py otherwise it will fail to import
the mach library.

--HG--
extra : rebase_source : 8077dd2fad4b78861add85febaf132ff77d6ad93