Document the logx parameter in Expr.nseries()

Add doctests. This parameter was introduced in
9c46974da12df56818020e29f76313fc0903ecc6 but it was never documented.
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
- Review comments from Aaron and Sergey incoroporated
- eval() refactored from csc() and sec() to ReciprocalTrigonometricFunction
- eval_rewrite_*() modified to avoid rewritting to reciprocal, if
  reciprocal function cannot handle rewrite request
- added a few more tests
Added Pablo Puente to AUTHORS
Added class documentation to ReciprocalTrigronometricFunction
- Issues fixed: 3608, 4067, 4068.  Added test cases for them.
- Added ReciprocalTrigonometricFunction_eval_nseries()
- Fixed ReciprocalTrigonometricFunction._eval_as_leading_term(). This fixes sec() and csc() wrong series.
whitespace removed
Simplify the last docstring example
Merge pull request #6 from skirpichev/certik-logx

Simplify the last docstring example
update MatrixExpr docstring
add list around theano_function outputs
raise NotImplementedError if theano.stacklists dne

At the time of this commit this feature in Theano is not yet released
and so depends on the development version.
subs(...).evalf -> evalf(subs=...)
Better explanation of the logx parameter

Also the doctests were polished.
Merge pull request #2444 from certik/logx

Document the logx parameter in Expr.nseries()
Implement membership test operator (method __contains__) for Order
Raise NotImplementedError when mixing Order at 0 and oo.
Fix Order(exp(x), x, oo) (issue 4108).