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/alias.rst

@@ -9,8 +9,8 @@ Synopsis
 .. synopsis::
 
     alias
-    alias [OPTIONS] NAME DEFINITION
-    alias [OPTIONS] NAME=DEFINITION
+    alias [--save] NAME DEFINITION
+    alias [--save] NAME=DEFINITION
 
 
 Description
@@ -21,7 +21,7 @@ Description
 ``fish`` marks functions that have been created by ``alias`` by including the command used to create them in the function description. You can list ``alias``-created functions by running ``alias`` without arguments. They must be erased using ``functions -e``.
 
 - ``NAME`` is the name of the alias
-- ``DEFINITION`` is the actual command to execute. The string ``$argv`` will be appended.
+- ``DEFINITION`` is the actual command to execute. ``alias`` automatically appends ``$argv``, so that all parameters used with the alias are passed to the actual command.
 
 You cannot create an alias to a function with the same name. Note that spaces need to be escaped in the call to ``alias`` just like at the command line, *even inside quoted parts*.
 
@@ -55,6 +55,6 @@ The following code will create ``rmi``, which runs ``rm`` with additional argume
 See more
 --------
 
-1. The :ref:`function <cmd-function>` builtin this builds on.
+1. The :ref:`function <cmd-function>` command this builds on.
 2. :ref:`Functions <syntax-function>`.
 3. :ref:`Function wrappers <syntax-function-wrappers>`.