Merge the duplicate API documentation

[eric-wieser]

Our API docs currently live in two places:

1. in the source itself, as:

   #some_file.py
   def some_func(...):
       """ The API docs """

   for example,
   

   galgebra/galgebra/ga.py

   Lines 366 to 374 in 3883eca

   	@staticmethod
   	def build(*args, **kwargs):
   	"""
   	Static method to instantiate geometric algebra and return geometric
   	algebra, basis vectors, and grad operator as a tuple.
   	"""
   	GA = Ga(*args, **kwargs)
   	basis = list(GA.mv())
   	return tuple([GA] + basis)

2. in module-components.rst, as:

   .. function:: some_func(...)
      :no-index:
   
      The other API docs

   for example,
   

   galgebra/doc/module-components.rst

   Lines 112 to 122 in 3883eca

   	.. method:: Ga.build(basis, g=None, coords=None, X=None, norm=False, debug=False)
   	:noindex:
   	The input parameters for ``Ga.build()`` are the same as for ``Ga()``. The difference is that in addition to returning the geometric algebra ``Ga.build()`` returns the basis vectors at the same time. Using ``Ga.build()`` in the previous example gives
   	.. code:: python
   	(r, th, phi) = coords = symbols('r,theta,phi', real=True)
   	basis = 'e_r e_theta e_phi'
   	g = [1, r**2, r**2*sin(th)**2]
   	(sp3d,er,eth,ephi) = Ga.build(basis,g=g,coord=coords,norm=True)

We should merge these together, by:

1. Manually merging the docstrings to preserve the best parts of each
2. Removing the contents of the .. function:: directive in module-components.rst, and changing it to

   .. autofunction:: some_file.some_func
      :no-index:
   

See #301 for an example of the type of change we should be fixing this with.