Add support for Poisson injector. Allows randomized load profiles.

Refactored PoissonInjector to use scanLeft

Switched to fixed-time variable-user model, using Lewis and Shedler's algorithm
Document PoissonInjection usage
Space before a star produces an unwanted blockquote
Merge pull request #1999 from notdryft/sphinx-doc

Documentation: Space before a star produces an unwanted blockquote
Fix Sphinx warnings
Fix cheat sheet typos
Cap caches size, close #2002
Fix test
Upded Gatling EL documentation
Upgrade AHC 1.9.0-BETA1, close #1982
Rename param into formParam, close #2003
Merge pull request #1990 from jamespic/poisson2

Core: Add support for Poisson injector. Allows randomized load profiles.
Don't highlight plain text as scala code
Merge pull request #2004 from notdryft/sphinx-highlight

Don't highlight plain text as scala code