Split documentation into multiple pages. (#722)

* Revive `com_interfaces.txt` from `3c916f61`.
Run `git revert 3c916f6` and cherry-pick `com_interfaces.txt`.

* `git mv docs/com_interfaces.txt docs/source/com_interfaces.rst`

* Remove the "Case sensitivity" section from `client.rst`, since it exists in `com_interfaces.rst`.

* Update Overview.

* Fix typo.

* Update section underline characters in `com_interfaces.rst`.

* Update indentations and enclosures in `com_interfaces.rst`.

* Improve code blocks in `com_interfaces.rst`.

* Add `com_interfaces` to `toctree::`.

* Fix code block in `server.rst`.

docs/source/client.rst

@@ -649,34 +649,6 @@ by ``py2exe``:
     >>> import comtypes.gen.Scripting
 
 
-Case sensitivity
-++++++++++++++++
-
-In principle, COM is a case insensitive technology (probably because
-of Visual Basic).  Type libraries generated from IDL files, however,
-do *not* always even preserve the case of identifiers; see for example
-http://support.microsoft.com/kb/220137.
-
-Python (and C/C++) are case sensitive languages, so |comtypes| is also
-case sensitive.  This means that you have to call
-``obj.QueryInterface(...)``, it will not work to write
-``obj.queryinterface(...)``.
-
-To work around the problems that you get when the case of identifiers
-in the type library (and in the generated Python module for this
-library) is not the same as in the IDL file, |comtypes| allows to have
-case insensitive attribute access for methods and properties in COM
-interfaces.  This behaviour is enabled by setting the
-``_case_insensitive_`` attribute of a Python COM interface to
-``True``.  In case of derived COM interfaces, case sensitivity is
-enabled or disabled separately for each interface.
-
-The code generated by the ``GetModule`` function sets this attribute
-to ``True``.  Case insensitive access has a small performance penalty,
-if you want to avoid this, you should edit the generated code and set
-the ``_case_insensitive_`` attribute to ``False``.
-
-
 Other stuff
 ***********