fix floating point problems in hmm class

subtracting 2 (nearly) equal floats can result in huge errors, just
assign 0.0 to differences of "equal" floats.

fix issue #14
float compare x < y => x-y < -DBL_EPSILON
split up tests for travis

prevents builds from failing due to time restrictions
update documentation
Merge pull request #21 from Garonenur/travis

Travis
Merge pull request #22 from Garonenur/hmm_32bit

Hmm 32bit
add refcount to multieoplist, cosmetics
change show fct to reflect different edit ops

cosmetics
add a backtrack fct to the xdrop class

returns a multieoplist
Merge pull request #23 from Garonenur/dw

add backtracking to xdrop class
remove gitweb script
change old gitweb links to github