Issue 3656: Implementation of fancy indexing in matrix
give Sparse an extract method; let Sparse use fancy indices
remove testing for slice in a2idx
edit submatrix doc and copy docs into sparse.py
Bump version to 0.7.4-git
Corrected cross product determinant representation.
Merge pull request #2641 from pestrickland/master

Mechanics documentation correction
Add Paul Strickland to the AUTHORS/aboutus. Welcome to SymPy!
watch for real and imag parts being equal in solve
Merge pull request #2643 from smichr/gh2642

watch for real and imag parts being equal in solve
Merge pull request #2622 from smichr/3565

Issue 3656: Implementation of fancy indexing in matrix
remove submatrix method
make out of range indices in Sparse raise IndexError
Lagrange method couldn't handle moments due to missing elif.
Merge pull request #2653 from jgoppert/lagrange-moment-fix

Lagrange method couldn't handle moments due to missing elif.
Fix Add.flatten when terms have S.NaN
Merge pull request #2652 from skirpichev/gh2633

Fix Add.flatten when terms have S.NaN
Merge pull request #2651 from smichr/submatrix

remove submatrix
Add James Goppert to AUTHORS/aboutus. Welcome to SymPy!
Merge branch 'master' into 0.7.4

Conflicts:
	.mailmap
	AUTHORS
	doc/src/aboutus.rst
	sympy/__init__.py