WIP: Refactor to simple parser approach

[ThomasWeinert]

After reading the open issues I started to refactor the source for them and it got a little out of hand. :-P

It is a complete refactoring, changing the approach to a small line parser for the files. Sampler.Files keeps track of the requested files and creates Sampler.File objects with named samples and lines. The Sampler.Line objects store the line content, number and type. It allows the files to be fetched and parsed once only. Sampler.Sample appends the selected snippets/lines.

• Implement Consider adding support for marking lines from a source files #8: mark lines using comments in the source file
• Implement Feature request: remove labels for full file #9: skip sample delimiter lines
• Implement Feature request: overlapping sections #10: allow overlapping sample sections
• Implement: output line numbers
• Implement: skip lines by number
• Implement: allow to mix names and line ranges in sample selector
• Implement: configure language specific patterns