Switch a hard-coded gemspec to Jeweler

[dblock]

Added jeweler, which makes generation of the gemspec declarative. Added a version accessible in Ruby.

[kslazarev]

Nice. I do some refactoring for test. If you have questions or proposals, write a comment below.

[kslazarev]

For example, for your opinion, where we must leave 'rake' and 'bundler' in Gemfile? In general or development section?

[dblock]

You can't put bundler in Gemfile, it's the one thing that has to be installed externally. Rake now warns you that it's not included but used and it's only needed in dev section.

[kslazarev]

Thank's, do this.