support QUIP wrapper API version query, relax hybrid restriction to allow hybrid/overlay, update docs

also fix some typos and formatting issues

In #514 it has been raised that the switching function that
ensures a smooth transition to the cutoff is only correct if
cutlj = 3.0. This patch gives users an opportunity to configure
the switching function together with the cutoff by specifying
the start of the transition region. Behaviour in the default case
remaing unchanged.
This allows users to specify larger cutoffs than 3 (which used to
have no effect) and get correct cutoff behaviour for values less
then 3.

reword the kspace_modify fftbench keyword docs to reflect the current state (i.e. off by default) of code