doc: convert printk-formats.txt to rst

Documentation/printk-formats.txt is a candidate for conversion to
ReStructuredText format. Some effort has already been made to do this
conversion even thought the suffix is currently .txt

Changes required to complete conversion

 - Move printk-formats.txt to core-api/printk-formats.rst
 - Add entry to Documentation/core-api/index.rst
 - Remove entry from Documentation/00-INDEX
 - Fix minor grammatical errors.
 - Order heading adornments as suggested by rst docs.
 - Use 'Passed by reference' uniformly.
 - Update pointer documentation around %px specifier.
 - Fix erroneous double backticks (to commas).
 - Remove extraneous double backticks (suggested by Jonathan Corbet).
 - Simplify documentation for kobject.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
[jc: downcased "kernel"]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/00-INDEX

@@ -346,8 +346,6 @@ prctl/
 	- directory with info on the priveledge control subsystem
 preempt-locking.txt
 	- info on locking under a preemptive kernel.
-printk-formats.txt
-	- how to get printk format specifiers right
 process/
 	- how to work with the mainline kernel development process.
 pps/

Documentation/core-api/index.rst

@@ -22,6 +22,7 @@ Core utilities
    flexible-arrays
    librs
    genalloc
+   printk-formats
 
 Interfaces for kernel debugging
 ===============================

lib/vsprintf.c

@@ -1834,7 +1834,8 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
  *
  * - 'x' For printing the address. Equivalent to "%lx".
  *
- * ** Please update also Documentation/printk-formats.txt when making changes **
+ * ** When making changes please also update:
+ *	Documentation/core-api/printk-formats.rst
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a