refactor(memmap)!: change behavioural flags to commands

This change factors out the following memory map tool flags into
independent commands:

- `--footprint` (becomes `memory footprint`)
- `--tree` (becomes `memory tree`)
- `--symbol` (becomes `memory symbol`)

So, for example, where previously you would generate the memory
footprint of a build with:

    memory --tree

You would now instead use:

    memory footprint

Any flags specific to a command (e.g. `--depth` for `tree`) must be
specified after the command, e.g.

    memory tree --depth 1

... instead of:

    memory --depth 1 tree

BREAKING-CHANGE: The image memory map visualization tool now uses
  commands, rather than arguments, to determine the behaviour of the
  script. See the commit message for further details.

Change-Id: I11d54d1f6276b8447bdfb8496544ab80399459ac
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/docs/tools/memory-layout-tool.rst b/docs/tools/memory-layout-tool.rst
index d9c358d..2506d2f 100644
--- a/docs/tools/memory-layout-tool.rst
+++ b/docs/tools/memory-layout-tool.rst
@@ -41,7 +41,7 @@
 
 .. code:: shell
 
-    $ poetry run memory -s
+    $ poetry run memory symbols
     build-path: build/fvp/release
     Virtual Address Map:
                +------------__BL1_RAM_END__------------+---------------------------------------+
@@ -116,14 +116,14 @@
 Memory Footprint
 ~~~~~~~~~~~~~~~~
 
-The tool enables users to view static memory consumption. When the options
-``-f``, or ``--footprint`` are provided, the script analyses the ELF binaries in
-the build path to generate a table (per memory type), showing memory allocation
-and usage. This is the default output generated by the tool.
+The tool enables users to view static memory consumption. When the ``footprint``
+command is provided, the script analyses the ELF binaries in the build path to
+generate a table (per memory type), showing memory allocation and usage. This is
+the default output generated by the tool.
 
 .. code:: shell
 
-    $ poetry run memory -f
+    $ poetry run memory footprint
     build-path: build/fvp/release
     +----------------------------------------------------------------------------+
     |                         Memory Usage (bytes) [RAM]                         |
@@ -150,13 +150,13 @@
 Memory Tree
 ~~~~~~~~~~~
 
-A hierarchical view of the memory layout can be produced by passing the option
-``-t`` or ``--tree`` to the tool. This gives the start, end, and size of each
-module, their ELF segments as well as sections.
+A hierarchical view of the memory layout can be produced by passing the ``tree``
+command to the tool. This gives the start, end, and size of each module, their
+ELF segments as well as sections.
 
 .. code:: shell
 
-    $ poetry run memory -t
+    $ poetry run memory tree
     build-path: build/fvp/release
     name                                       start        end       size
     bl1                                            0    400c000    400c000
@@ -209,7 +209,7 @@
 
 .. code::
 
-    $ poetry run memory -t --depth 2
+    $ poetry run memory tree --depth 2
     build-path: build/fvp/release
     name                          start        end       size
     bl1                               0    400c000    400c000