top: Replace upip with mip everywhere.

Updates all README.md and docs, and manifests to `require("mip")`.

Also extend and improve the documentation on freezing and packaging.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

docs/develop/gettingstarted.rst

@@ -322,7 +322,8 @@ tests
 
 tools
 
-  Contains helper tools including the ``upip`` and the ``pyboard.py`` module.
+  Contains scripts used by the build and CI process, as well as user tools such
+  as ``pyboard.py`` and ``mpremote``.
 
 examples
 

docs/develop/optimizations.rst

@@ -25,6 +25,8 @@ into the firmware image as part of the main firmware compilation process, which
 the bytecode will be executed from ROM. This can lead to a significant memory saving, and
 reduce heap fragmentation.
 
+See :ref:`manifest` for more information.
+
 Variables
 ---------