4094: add note about chop

While checking this I noticed that chopping occurs for
any number in an expression, not only the final result.
This is sub-optimal. e.g. (pi/65).n(chop=.01) rounds to
zero because the 1/65 rounds to less than 0.02 and is
replaced with zero even though if the rounding was delayed
until the multiplication by pi occured, it wouldn't have
been rounded. I did not clutter the docs with this detail, however.
Merge pull request #2576 from smichr/docs

4094: add note about chop in docs
preserve shape for 0-sized Matrices
Merge pull request #2598 from smichr/4102

preserve shape for 0-sized Matrices
check solution to issue 3994
Merge pull request #4 from smichr/3994

check solution to issue 3994
Merge pull request #2570 from rlamy/pydy_bench

KanesMethod optimisation
Merge pull request #2594 from zanzibar7/issue3994

Issue 3994 fix
Install scipy deps, including blas, gfortran, etc
Merge pull request #2500 from skirpichev/3265-eval-lt-fix

Fix issue 3265 (simplify output of Add._eval_as_leading_term)
Merge pull request #15 from skirpichev/mrocklin-computation-docs

Try to install scipy deps, including blas, gfortran, etc
semicolons!
Merge pull request #16 from skirpichev/mrocklin-computation-docs

fix travis failures
Merge pull request #2476 from skirpichev/pr343-fix

Fix fact extraction from composite assumptions
Merge pull request #2463 from skirpichev/2085-bounded-x-limit

Fix limit heuristics for real, bounded symbols
Merge branch 'master' into 2625-complex-comparison
Raise an exception in _isright method (refactored to static class method), if t_area.is_nonpositive is None
Use print functions in fabfile.py
Re-enable fabvenv stuff
Use @task in the fabfile

This fixes issue 4052.