New source tools: booleanized, pre_periodic_filtered & post_periodic_filtered

Also adds extra parameter validation to the existing source tools, adds input
min and max to inverted, and adds many more source tools unit tests.

docs/api_tools.rst

@@ -10,7 +10,7 @@ the :attr:`~gpiozero.SourceMixin.source` and
 library. These utility routines are in the ``tools`` module of GPIO Zero and
 are typically imported as follows::
 
-    from gpiozero.tools import scaled, negated, conjunction
+    from gpiozero.tools import scaled, negated, all_values
 
 Given that :attr:`~gpiozero.SourceMixin.source` and
 :attr:`~gpiozero.ValuesMixin.values` deal with infinite iterators, another
@@ -29,6 +29,8 @@ Single source conversions
 
 .. autofunction:: absoluted
 
+.. autofunction:: booleanized
+
 .. autofunction:: clamped
 
 .. autofunction:: inverted
@@ -37,8 +39,12 @@ Single source conversions
 
 .. autofunction:: post_delayed
 
+.. autofunction:: post_periodic_filtered
+
 .. autofunction:: pre_delayed
 
+.. autofunction:: pre_periodic_filtered
+
 .. autofunction:: quantized
 
 .. autofunction:: queued
@@ -56,10 +62,10 @@ Combining sources
 
 .. autofunction:: averaged
 
-.. autofunction:: summed
-
 .. autofunction:: multiplied
 
+.. autofunction:: summed
+
 Artificial sources
 ==================