update MatrixExpr docstring
Implement membership test operator (method __contains__) for Order
bessel: _eval_is_real
Test is_real for besselx with real arguments
Test as_real_imag for besselx with real args
Add Tuomas Airaksinen to the AUTHORS/aboutus. Welcome to SymPy!
Delete generic BesselBase._eval_is_real and add specific ones for besselx
bessel: fix is_real tests
Merge pull request #2616 from skirpichev/order-contains-op

Implement membership test operator (method __contains__) for Order, just like Set
2401: Fix pretty-printing of Lambda.

In [1]: Lambda((x, y), x*y)+1
Out[1]: 1 + ((x, y) ↦ x⋅y)

In [2]: Lambda(x, x**2)**2
Out[2]:
        2
⎛     2⎞
⎝x ↦ x ⎠

In [3]: RootSum(x**5 + 11*x - 2, Lambda(z, exp(z)))
Out[3]:
       ⎛ 5                  z⎞
RootSum⎝x  + 11⋅x - 2, z ↦ ℯ ⎠
Merge pull request #2623 from skirpichev/rlamy-print-Lambda

pretty-printing of Lambda (issue 2401)
add section titles to MatrixExpr docstring
Merge pull request #2619 from skirpichev/tuomas2-besselj-CLEANUP

A replacement for #2566
Merge pull request #2603 from mrocklin/matexpr-docstring

update MatrixExpr docstring
Delete ancient type cast
Add note: all limit points should be either 0 or oo
Make definition consistent: \lim -> \lim\sup
Add examples
Merge branch 'master' into order-fix-syntax2
Add missing imports for docstring examples