docs: omnibus cleanup

Includes harmonizing the display of options and arguments, standardising
terminology, using the envvar directive more broadly, adding help options to all
commands that support them, simplifying some language, and tidying up multiple
formatting issues.

string documentation is not changed.

doc_src/cmds/block.rst

@@ -8,7 +8,8 @@ Synopsis
 
 .. synopsis::
 
-    block [OPTIONS]
+    block [(--local | --global)]
+    block --erase
 
 Description
 -----------
@@ -21,6 +22,8 @@ The block can be removed. Any events which triggered while the block was in plac
 
 Event blocks should not be confused with code blocks, which are created with ``begin``, ``if``, ``while`` or ``for``
 
+Without options, the ``block`` command acts with function scope.
+
 The following options are available:
 
 **-l** or **--local**
@@ -32,6 +35,9 @@ The following options are available:
 **-e** or **--erase**
     Release global block.
 
+**-h** or **--help**
+    Displays help about using this command.
+
 Example
 -------
 ::