v0.4.0 -- Combinatorial fuzzing and fuzzing CLI

Features

• Fuzzing CLI -- Use main_helper() to use boofuzz's generic fuzzing CLI with your script.
• Combinatorial fuzzing -- now fuzzes multiple mutations at once by default.
• Test cases can now be specified and re-run by name.
• Implemented visual request-graph rendering functions for Session.
• Added to web UIL: runtime, exec speed, current test case name.
• Added simple custom checksum and example usage.
• Added Simple primitive that uses only the specified values for fuzzing.
• Added Float primitive with support for IEEE 754 encoding.
• Added an example for s_float/Float usage.

Fixes

• Clarified documentation of custom checksum function for Checksum primitive.
• String and RandomData primitives now use a local and independent instance of random.
• The minimum supported Python version is now 3.6.
• Fixed two memory leaks in the fuzz logger.