improve convergence by doubling the burn-in

Improve convergence by running two burn-in phases, adjusting the jump
distribution widths after each. This insulates the final run from a really
wrong initial jump distribution.

Also includes a few bug fixes.
Removed partialfill specific code
Merge remote-tracking branch 'mastbaum/cleanup' into partialfill

Conflicts:
	src/plots.cpp
	src/sxmc.cpp
Added ability to load data from ttrees