Update configuration for build step
Add Config#run method for DSL
Add test for Mamiya::Steps::Build
Add empty class
extract Build step packaging spec to Package spec

I noticed Build#run! have too much responsibilities...
Add empty implementation of Mamiya::Package
Add pending spec to not forget
Add exception class
Complete package_spec
Implement Mamiya::Package
Fix build_spec.rb
Add missing dependency
Implement Mamiya::Steps::Build
bz2 -> gz

- gz is faster than bzip2

  - bzip2 can reduce filesize more, but takes too long
Use tar -C option instead of running with chdir
Merge pull request #2 from sorah/builder

Implementation of Build step