BUG: Rolling back Logbook version due to incompatibility with Processor/filter
interactions.
DOC: Add version and download counter to README.
DOC: Wrong link for badges.
BLD: Add coverage integration.
DOC: Add coverage badge to README.
BLD: Second try at coverage integration.
MAINT: One way to set sim_params and data_frequency.

There were sevaral places you could supply sim_params
in TradingAlgorithm (__init__, run). This got confusing
as its not clear who updated what and which one was the
correct one to use at each time.

Then there were to ways to define data_frequency, one in
__init__() and one in the sim_params which also added code
complexity.

This refactor makes it explicit that sim_params are to be
passed to __init__() only. Moreover, data_frequency is
only stored in sim_params. For backwards compatibility,
it can still be supplied separately but will link to
the one in sim_params.

In addition, perf_tracker only gets initialized in one place:
_create_generator() which should also make the various ways
of running an algorithm more deterministic.

This also fixes a bug with SimulationParameters where
you could not change the period_start. Unfortunately, the
current implementation still requieres an implicit call to
update the internal variables.
MAINT: Remove unused annualizer code.