Add first version of CMake framework code

This commit adds the core elements of the framework and documentation:
 - Map utility: store key-value pairs.
 - Group utility: store build configuration options.
 - STGT API: describe the targets.
 - Compiler abstraction functions for GCC.
 - Other helper functions.
 - New CMake system type called "Embedded", using correct output file
   prefixes and extensions.
 - Sphinx based documentation which includes:
    - licensing information
    - version numbering policy
    - documentation on how-to build the documentation

In addition the following utility files are added:
  - .editorconfig
  - .gitignore

Change-Id: If19a171ef066775d3544fba82f1cc70a5fb0e7d7
Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Co-authored-by: Gyorgy Szing <gyorgy.szing@arm.com>
Co-authored-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/doc/index.rst b/doc/index.rst
new file mode 100644
index 0000000..d57d815
--- /dev/null
+++ b/doc/index.rst
@@ -0,0 +1,43 @@
+Welcome to TF-A CMake Framework's documentation!
+================================================
+
+.. toctree::
+   :maxdepth: 1
+   :caption: Contents:
+
+   Home<self>
+   license
+   change-log
+   contributing
+   coding-guidelines
+   maintainers
+   user_guide
+   map
+   group
+   stgt
+   gcc
+   utils
+   docs-build
+   software_requirements
+   versioning_policy
+   glossary
+   todo
+
+The CMake Framework is a set of CMake functions organised into logical modules,
+adding missing features to CMake and standardizing the usage of existing ones.
+The framework's primary purpose is to simplify creating cross-compiled, embedded
+projects.
+
+The current version of the framework is version |release|. For details about
+changes between versions please refer to the :ref:`Change Log & Release Notes`.
+
+For information on planned changes and issues to be addressed please refer to
+:ref:`TODO list`.
+
+.. todo:: Expand general description of the framework.
+
+--------------
+
+*Copyright (c) 2019-2020, Arm Limited and Contributors. All rights reserved.*
+
+SPDX-License-Identifier: BSD-3-Clause