docs: namespaces: convert to ReST

Rename the namespaces documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

There are two upper case file names. Rename them to
lower case, as we're working to avoid upper case file
names at Documentation.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/namespaces/compatibility-list.txt → Documentation/namespaces/compatibility-list.rst

-	Namespaces compatibility list
+=============================
+Namespaces compatibility list
+=============================
 
 This document contains the information about the problems user
 may have when creating tasks living in different namespaces.
@@ -7,13 +9,16 @@ Here's the summary. This matrix shows the known problems, that
 occur when tasks share some namespace (the columns) while living
 in different other namespaces (the rows):
 
-	UTS	IPC	VFS	PID	User	Net
+====	===	===	===	===	====	===
+-	UTS	IPC	VFS	PID	User	Net
+====	===	===	===	===	====	===
 UTS	 X
 IPC		 X	 1
 VFS			 X
 PID		 1	 1	 X
 User		 2	 2		 X
 Net						 X
+====	===	===	===	===	====	===
 
 1. Both the IPC and the PID namespaces provide IDs to address
    object inside the kernel. E.g. semaphore with IPCID or
@@ -36,4 +41,3 @@ Net						 X
    even having equal UIDs.
 
    But currently this is not so.
-

Documentation/namespaces/index.rst

+:orphan:
+
+==========
+Namespaces
+==========
+
+.. toctree::
+   :maxdepth: 1
+
+   compatibility-list
+   resource-control

Documentation/namespaces/resource-control.txt → Documentation/namespaces/resource-control.rst

+===========================
+Namespaces research control
+===========================
+
 There are a lot of kinds of objects in the kernel that don't have
 individual limits or that have limits that are ineffective when a set
 of processes is allowed to switch user ids.  With user namespaces