docs: Correct typos in documentation (#592)

doc/design/color_space.rst

@@ -45,7 +45,7 @@ Besides the standard layouts, it also provides:
 - ``abgr_layout_t``
 - ``argb_layout_t``
 
-As an example, here is how GIL defines the RGBA color space::
+As an example, here is how GIL defines the RGBA color space:
 
 .. code-block:: cpp
 
@@ -58,7 +58,7 @@ As an example, here is how GIL defines the RGBA color space::
 The ordering of the channels in the color space definition specifies their
 semantic order. For example, ``red_t`` is the first semantic channel of
 ``rgba_t``. While there is a unique semantic ordering of the channels in a
-color space, channels may vary in their physical ordering in memory
+color space, channels may vary in their physical ordering in memory.
 
 The mapping of channels is specified by ``ChannelMappingConcept``, which is
 an MPL random access sequence of integral types.

doc/design/concepts.rst

@@ -8,7 +8,7 @@ algorithmic guarantees. For example, GIL class ``pixel`` is a model of GIL
 ``PixelConcept``. The user may substitute the pixel class with one of their
 own, and, as long as it satisfies the requirements of ``PixelConcept``,
 all other GIL classes and algorithms can be used with it.
-See more about concepts is avaialble at
+See more about concepts at
 `Generic Programming in ConceptC++ <https://web.archive.org/web/20160324115943/http://www.generic-programming.org/languages/conceptcpp/>`_
 
 In this document we will use a syntax for defining concepts that is described

doc/design/point.rst

@@ -39,7 +39,7 @@ in which both dimensions are of the same type:
       typename value_type = axis<0>::type;
 
       const value_type& operator[](const T&, size_t i);
-          value_type& operator[](      T&, size_t i);
+            value_type& operator[](      T&, size_t i);
 
       value_type x,y;
   };