Merge pull request #3 from nbraud/master

Ignore Emacs' temp files
Some punctuation.
Change the way the rope accumulator is constructed for the tyxml backend.
Correct the name and synopsis in the oasis file ... silly me.
Create a new modular library for the various graphical stuff.
Update the documentation with the new syntax for lsystems.
Return the symbol env alone rather than the package senv.
Raise an exception when a negative integer is given as generation number.
Separate lsystem evaluation on smaller operation in the engine.
Move all stream stuff into a separate file and expose them through the interface. Update the documentation accordingly.
Small fix in the documentation, works better with '-colorize-code'.
Expose the internal engine as a functor through the interface.
Add a proper interface to Glilis. Update backends to respect it.
Add an interface (and a documentation) to the tyxml backend.
Add an interface (and a documentation) to the cairo backend.
Remove the surface argument from the cairo turtle.
Small change in the bank for a simpler von koch curve
Add an intro to the documentation. Update the build process accordingly.
Small modification in the documentation (to avoid duplications).
Remove the profiling informations.