doc: Update various process documents ...

Most of the changes consist in using the new code owners terminology
(from [1]).

[1] https://developer.trustedfirmware.org/w/collaboration/project-maintenance-process/

Change-Id: Icead20e9335af12aa47d3f1ac5d04ca157b20c82
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

doc: Split and expand coding style documentation ...

This patch expands the coding style documentation, splitting it
into two documents: the core style rules and extended guidelines.
Note that it does not redefine or change the coding style (aside
from section 4.6.2) - generally, it is only documenting the
existing style in more detail.

The aim is for the coding style to be more readable and, in turn,
for it to be followed by more people. We can use this as a more
concrete reference when discussing the accepted style with external
contributors.

Change-Id: I87405ace9a879d7f81e6b0b91b93ca69535e50ff
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
Signed-off-by: Petre-Ionut Tudor <petre-ionut.tudor@arm.com>

doc: Split the User Guide into multiple files ...

The User Guide document has grown organically over time and
now covers a wide range of topics, making it difficult to
skim read and extract information from. Currently, it covers
these topics and maybe a couple more:

- Requirements (hardware, tools, libs)
- Checking out the repo
- Basic build instructions
- A comprehensive list of build flags
- FIP packaging
- Building specifically for Juno
- Firmware update images
- EL3 payloads
- Preloaded BL33 boot flow
- Running on FVPs
- Running on Juno

I have separated these out into a few groups that become new
documents. Broadly speaking, build instructions for the tools,
for TF-A generally, and for specific scenarios are separated.
Content relating to specific platforms (Juno and the FVPs are
Arm-specific platforms, essentially) has been moved into the
documentation that is specific to those platforms, under
docs/plat/arm.

Change-Id: Ica87c52d8cd4f577332be0b0738998ea3ba3bbec
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Convert internal links to RST format ...

Currently links between documents are using the format:

<path/to/><filename>.rst

This was required for services like GitHub because they render each
document in isolation - linking to another document is like linking
to any other file, just provide the full path.

However, with the new approach, the .rst files are only the raw
source for the documents. Once the documents have been rendered
the output is now in another format (HTML in our case) and so,
when linking to another document, the link must point to the
rendered version and not the .rst file.

The RST spec provides a few methods for linking between content.
The parent of this patch enabled the automatic creation of anchors
for document titles - we will use these anchors as the targets for
our links. Additional anchors can be added by hand if needed, on
section and sub-section titles, for example.

An example of this new format, for a document with the title
"Firmware Design" is :ref:`Firmware Design`.

One big advantage of this is that anchors are not dependent on
paths. We can then move documents around, even between directories,
without breaking any links between documents. Links will need to be
updated only if the title of a document changes.

Change-Id: I9e2340a61dd424cbd8fd1ecc2dc166f460d81703
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

Further fixes to documentation links ...

Change-Id: Ib021c721652d96f6c06ea18741f19a72bba1d00f
Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>

doc: Reword document titles ...

This patch attempts to standardise the document titles as well as
adding titles to documents that were missing one. The aim is to
remove needless references to "TF-A" or "Trusted Firmware" in the
title of every document and to make sure that the title matches
with the document content.

Change-Id: I9b93ccf43b5d57e8dc793a5311b8ed7c4dd245cc
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Move documents into subdirectories ...

This change creates the following directories under docs/
in order to provide a grouping for the content:

- components
- design
- getting_started
- perf
- process

In each of these directories an index.rst file is created
and this serves as an index / landing page for each of the
groups when the pages are compiled. Proper layout of the
top-level table of contents relies on this directory/index
structure.

Without this patch it is possible to build the documents
correctly with Sphinx but the output looks messy because
there is no overall hierarchy.

Change-Id: I3c9f4443ec98571a56a6edf775f2c8d74d7f429f
Signed-off-by: Paul Beesley <paul.beesley@arm.com>