Always running the possibly very expensive preparation code when
a benchmark object is created is not reasonable when benchmarks
should only be summarized.

Don't export a singleton object in the definiton.
An object is now created when the Benchmark should be executed, thus
we don't need a prepare method this can be done in __init__

* rename src directory to allocbench
* make global variable names UPPERCASE
* format a lot of code using yapf
* use lowercase ld_preload and ld_library_path as Allocator members
* name expected Errors 'err' and don't raise a new Exception
* disable some pylint messages

A allocator implementation is analyzed by prepending chattymalloc.so.