Build: Semantic versioning support

This patch modifies the project's versioning
schema to support semantic versioning.

The new schema going forward is:

<Major>.<Minor>.Hotfix>

The patch updates:

• The TF-M version macros
* Previous releases' documentation
* The version detection logic for documentation to support
  old and new schema

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
Change-Id: I6baa0cab849d656c8d756d4a70c10c258ef3001c
diff --git a/docs/contributing/release_process.rst b/docs/contributing/release_process.rst
index b47913c..8b6d196 100644
--- a/docs/contributing/release_process.rst
+++ b/docs/contributing/release_process.rst
@@ -25,6 +25,18 @@
 Although this document specifies the release cadence, this does not preclude
 an adhoc release for specific project requirements.
 
+Release Version Scheme
+----------------------
+
+Trusted Firmware-M uses a semantic versioning scheme. A version number is
+compiled as a dot separated set of numbers:
+
+**TF-Mv<MAJOR>.<MINOR>.<HOTFIX>**
+
+- <MAJOR>: Major release version for significant feature and API changes.
+- <MINOR>: Minor release version for incremental features and API changes.
+- <HOTFIX>: Used only for backporting **critical bug fix/security patches**.
+
 --------------
 
 *Copyright (c) 2020, Arm Limited. All rights reserved.*
diff --git a/docs/introduction/readme.rst b/docs/introduction/readme.rst
index b5ddecc..b53c12c 100644
--- a/docs/introduction/readme.rst
+++ b/docs/introduction/readme.rst
@@ -188,6 +188,10 @@
 | v1.1        | 2020-07-15   | 1.1 release        | 1f960947          |
 +-------------+--------------+--------------------+-------------------+
 
+Please refer to
+:ref:`docs/contributing/release_process:Release Version Scheme` for interpreting
+version numbers.
+
 .. _Cortex-M33: https://developer.arm.com/ip-products/processors/cortex-m/cortex-m33
 .. _Cortex-M23: https://developer.arm.com/ip-products/processors/cortex-m/cortex-m23
 .. _Cortex-M55: https://developer.arm.com/ip-products/processors/cortex-m/cortex-m55