Expansions for harmonic numbers at general rational arguments n + p/q

In [2]: harmonic(2/S(3))
Out[2]: harmonic(2/3)

In [3]: expand_func(_)
(0, 2, 3)
Out[3]: -log(6) + 2*Sum(log(sin(_k*pi/3))*cos(4*_k*pi/3), (_k, 1, 1)) + sqrt(3)*pi/6 + 3*Sum(1/(3*_k + 2), (_k, 0, 0))

In [4]: pprint(_)
              1                                            0
             ____                                         ____
             ╲                                            ╲
              ╲      ⎛   ⎛k⋅π⎞⎞    ⎛4⋅k⋅π⎞     ___         ╲      1
               ╲  log⎜sin⎜───⎟⎟⋅cos⎜─────⎟   ╲╱ 3 ⋅π        ╲  ───────
-log(6) + 2⋅   ╱     ⎝   ⎝ 3 ⎠⎠    ⎝  3  ⎠ + ─────── + 3⋅   ╱  3⋅k + 2
              ╱                                 6          ╱
             ╱                                            ╱
             ‾‾‾‾                                         ‾‾‾‾
            k = 1                                        k = 0

In [5]: _.doit()
Out[5]: -log(6) - log(sqrt(3)/2) + sqrt(3)*pi/6 + 3/2

In [6]: simplify(_)
Out[6]: log(sqrt(3)/9) + sqrt(3)*pi/6 + 3/2

In [7]: _.n()
Out[7]: 0.758981249114944

In [8]: harmonic(2/S(3))
Out[8]: harmonic(2/3)

In [9]: _.rewrite(polygamma)
Out[9]: -3*log(3)/2 + sqrt(3)*pi/6 + 3/2

In [10]: _.n()
Out[10]: 0.758981249114944
Clean up harmonic number tests
Tests for expansion of harmonic numbers at rational arguments
Documentation for rational argument expansion
Improve values of harmonic numbers at infinity
More tests for harmonic numbers
Fix equality of harmonic(n, 1) == harmonic(n) for arbitrary n
Fix limit of harmonic numbers
Add xfail for harmonic number limit
Small chnge to the intersection method of a polygon
Merge pull request #7441 from akshayah3/geometry

Small change to the intersection method of a polygon
Merge pull request #7422 from raoulb/rational_harmonic

Expansions for harmonic numbers at general rational arguments n + p/q
fix redirection links
This work was started by Taranjeet Singh <reachtotj@gmail.com>
Merge pull request #7436 from debugger22/staranjeet-link_fix

Redirection links fixed