Wharfie

support host commands for toolchain generation

[#14] error while apt-get install: "... -y was used without --allow-unauthenticated"
- issue and apt-get update before fetching the rest. Without an updated package list, this makes no sense anyway.

During some tests with a Dockerfile for check_mk, I implemented a few compatibility commands (EXPOSE, ARG, WORKDIR)

[#7] Support the commands COPY and ENTRYPOINT
- I messed up CMD and ENTRYPOINT

#7 Support the commands COPY and CMD

[#10]
- Support building of toolchains in one run.
- fixed build abortion
- fixed double creation of output file for temporary targets

added missing return statement for toolchains

[#8] experimental implementation of incremental/multi-level build.
Actually it seems as tar has still problems with it. I can't avoid that tar thinks that s.th. is renamed, even if it is not.
In my tests I found no problems, except the warning from tar until now. But I added it as a command line option anyway, to be safe.

By-the-way I fixed the handling of files in ADD a bit.
- URLs are supported now
- Implicite makerules don't interfer anymore with ADD

restructured the main python script into submodules (curently only makefile generation and wharfile actions)