Merge pull request #1 from yosefm/master

Omnibus update, nobody reviewed, don't come crying later.
Merge pull request #2 from yosefm/ptvis_mem

Ptvis memory consumption
Fix: wrong file opened by sequence reading test, found by Alex.
Merge pull request #3 from yosefm/working_branch

Saving configuration. Merged with fix to the bug pointed by Alex.
ptv_is reading by an iterator, so we don't have to hold everything in memory if not completely necessary.
Use the new iter_trajectories_ptvis when possible to save memory, e.g. in saving a trajectory table without loading all trajectories first.
Small fix to prevent bombs on logarithmic plots.
Fix: data directory relative to project root.
Different minimal trajectory length for format that require forward difference velocity calculation (ptvis)
added the test that fails with the min length less than 2
fixed the problem with the xuap that requires min. length of 2 (not 1)
Merge pull request #4 from yosefm/iter_trajects

Iterate ptv_is trajectories instead of reading entire list at once.
Work around bug in backward-compatibility of newer PyTables version.
Merge branch 'master' of https://github.com/OpenPTV/postptv
fix bad default trajectory length in trajectories()
Merge commit 'e85eaaf5db398581afef70eec54aa6ec78b3864d'

* commit 'e85eaaf5db398581afef70eec54aa6ec78b3864d':
  fix bad default trajectory length in trajectories()
  Work around bug in backward-compatibility of newer PyTables version.
  fixed the problem with the xuap that requires min. length of 2 (not 1)
  added the test that fails with the min length less than 2
  Different minimal trajectory length for format that require forward difference velocity calculation (ptvis)
  Fix: data directory relative to project root.
  Small fix to prevent bombs on logarithmic plots.
  Use the new iter_trajectories_ptvis when possible to save memory, e.g. in saving a trajectory table without loading all trajectories first.
  ptv_is reading by an iterator, so we don't have to hold everything in memory if not completely necessary.
  Fix: wrong file opened by sequence reading test, found by Alex.