BF: do not crash if pprocess is not there and nproc=None
ENH+PY3: use // for integer division
PL: indent
BF: do not import hdf5 when external not present
PY3+RF: Improved Python3 compatibility
ENH: print error message with "%s", not "%r"
ENH+NF: improved and new __str__ functions
ENH+BF: proper conversion of linear indices to integer array
ENH: check for NaNs in coordinate equality comparison
ENH: more use of "%s" rather than "%r" in error messages
BF: type (forgot "x" in "xor")
Merge branch 'master' into _tent/surfing
ENH: more consistent printing behaviour (with parentheses)
ENH: briefer __str__ function
RF: use np.logical_not instead of "-"
Merge pull request #146 from nno/_tent/surfing

minor fixes to surface-based coding