Add MISRA.md (#35)

* Add MISRA.md from coreMQTT

* Change MISRA.md for the agent

* Apply suggestions from code review

Co-authored-by: Oscar Michael Abrina <[email protected]>

MISRA.md

@@ -0,0 +1,26 @@
+# MISRA Compliance
+
+The coreMQTT Agent library files conform to the [MISRA C:2012](https://www.misra.org.uk/MISRAHome/MISRAC2012/tabid/196/Default.aspx)
+guidelines, with some noted exceptions. Compliance is checked with Coverity static analysis.
+Deviations from the MISRA standard are listed below:
+
+### Ignored by [Coverity Configuration](tools/coverity/misra.config)
+| Deviation | Category | Justification |
+| :-: | :-: | :-: |
+| Directive 4.5 | Advisory | Allow names that MISRA considers ambiguous (such as LogInfo and LogError) |
+| Directive 4.8 | Advisory | Allow inclusion of unused types. Header files from coreMQTT may define types that are not used by the agent. |
+| Directive 4.9 | Advisory | Allow inclusion of function like macros. The `assert` macro is used throughout the library for parameter validation, and logging is done using function like macros. |
+| Rule 2.3 | Advisory | Allow unused types. Both the agent and coreMQTT headers define types that are not directly used by the library but are still intended to be used by the application. |
+| Rule 2.4 | Advisory | Allow unused tags. Some compilers warn if types are not tagged. |
+| Rule 2.5 | Advisory | Allow unused macros. Library headers may define macros intended for the application's use, but are not used by a specific file. |
+| Rule 3.1 | Required | Allow nested comments. C++ style `//` comments are used in example code within Doxygen documentation blocks. |
+| Rule 11.5 | Advisory | Allow casts from `void *`. Fields such as command parameters are passed as `void *` for generalization and must be cast to the correct data type before use. |
+
+### Flagged by Coverity
+| Deviation | Category | Justification |
+| :-: | :-: | :-: |
+| Rule 8.7 | Advisory | API functions are not used by the library outside of the files they are defined; however, they must be externally visible in order to be used by an application. |
+| Rule 8.13 | Advisory | Functions that are passed as pointers to coreMQTT or the agent must exactly match function signatures with the pointer type definition, so `const` modifiers cannot be added even if a specific function implementation does not modify a given parameter. |
+
+### Suppressed with Coverity Comments
+*None.*