Faster ``minpoly`` using composed sum.

Added power series functions on "ring.PolyElement" objects.
small changes in the documentation; used ``as_int``
Piecewise: added as_expr_set_pair property
Change version to 0.7.5.rc1
used ``giant_steps`` from ``mpmath``
Update .mailmap
(Retroactively) add Buck Shlegeris to AUTHORS/aboutus. Welcome to SymPy!
Fix Buck Shlegeris's position in the AUTHORS/aboutus files
Add Edward to AUTHORS/aboutus. Welcome to SymPy!
Add librsvg2-bin to fabfile, needed to build the docs
Website uploading should only be done in the final release
Add sympy.physics.vector.tests to setup.py
Merge pull request #2630 from pernici/mp5

faster minpoly using composed sum
use giant_steps in expr.py
Using u() instead of u''.
Merge pull request #2919 from moorepants/0.7.5

Using u() instead of u''.
Fix indentation
Add functions from calculus module to sphinx docs
fix typo in err message
block imaginary coordinates for Point

The computations that are done in geometry assume that
the points are real. Without placing undue stress on the
computations by checking this every time, a check is done
only when the coordinates are numbers. Of course, there
is nothing to stop one from using imaginary points in
an expression obtained from geometry, but one should not
be doing that.