Added methods to Vector

Vector and Dyadic now have the .doit() method, which calls .doit() on all of
the expressions which make up the vector. The .simplify() method was also
added, and it functions the same way.

Also, Vector and Dyadic .subs() now behaves more consistently compared to the
rest of SymPy.
Switched output order on partial velocity function

The previous output order was a list of lists with the order:
speeds x velocities
and now it has the order
velocities x speeds
Changed an interface in mechanics.

Kane -> KanesMethod; Also, KanesMethod now takes almost all info upon
initialization, to match the incoming LagrangesMethod. There are also the
associated changes in the documentation.

Also, one of the methods was significantly cleaned up. Some associated methods
in other classes needed stronger checking implemented also.
Made changes/correction re PR 1482 in mechanics

Some spelling changes, fixed some Sphinx documentation, partial_velocity now
takes in a ReferenceFrame.
combinatorics/partitions: First commit. Added init file.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added integer partition as a class and
added facility to compare instances of integer partitions.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added a routine to generate a random
partition.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added doctests for some routines.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to compute RGS of a
partition.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to compute conjugate of a
partition.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added another implementation of the
conjugate partition algorithm.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to find out Ferrers
representation.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added method to compute a partition from
a restricted growth string.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to check for self conjugacy
of a partition.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to compute the total
number of RGS possible for a given set size.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Implemented a method to enumerate the
generalized restricted growth strings.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to compute the unranked
partition for a given superset size.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to rank a RGS.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to compute rank of a
partition on the basis of its RGS.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>
combinatorics/partitions: Added routine to enable comparison of
partitions on the basis of its rank.

Signed-off-by: Saptarshi Mandal <sapta.iitkgp@gmail.com>