Document the logx parameter in Expr.nseries()

Add doctests. This parameter was introduced in
9c46974da12df56818020e29f76313fc0903ecc6 but it was never documented.
Docs updated
Intro and module structure completed.
Finished the tutorial
Fixed a typo
Fixed a typo
Fixed a doctest
Fixed Sphinx errors
Fixed the Docs
Few typos fixed
Matrix equation updated
Docs moved to Sphinx
Evaluate more terms for Laurent power series.  Fix issue 2555.
Add test for issue 2555
Merge branch 'master' into 2555-residue

Conflicts:
	sympy/series/tests/test_nseries.py
	sympy/series/tests/test_residues.py
Fix heuristic for Laurent series
Add test for github's issue 2519
csc(), sec(): Added missing functions to these trigonometric functions

Previous implementation of csc() and sec() was missing most of the methods
required to work with simplify(), eval(), rewrite(), series().
This implementation reuses partly the implementation of the functions in
sin() and cos(). This is done through an intermediate base class
ReciprocalTrigonometricFunction which csc and sec now subclass.
Removed unnecesary comment #
Solve documentation test error