LineNumber markers and other source-code information #70

So this is pretty self-explanatory.

There are artifacts of the original code that are sort of a common practice to include in jars and there are some that aren't.

• Source file entry. Indicates the name of the file which the class was compiled from.
• LineNumber markers. These are used in stack traces.
• CharacterRanges. These are much less common then linenumbers and probably would take a lot of space, so I would only include them in debug build.
• Docs. Interestingly enough, they are usually built into a different jar, compiled as html (so you don't have to transform rust docs into javadocs, just compile to html and bind). That would be especially useful for library developers, which usually have to ship all three: sources, binaries and docs.

Funnily enough, in the next issue I will complain about the binary size, so I probably all of this should be optional.