Remove comments in kernel.c
Add document for kernel internals
Update kernel-internal.md
Revise documentation/kernel-internal.md
WIP: Implement dynamic memory allocation

TODO: Unit test for memory allocation
Change naming and minor modification to improve readablity
shell.c: remove unneeded iteration in find_events()
shell.c: rename find_event to hist_expand
shell.c: improve readabily in environment variables handling
Revise documentation/kernel-internal.md
Fix warning: writing to APSR without specifying a bitmask is deprecated

Reference: 2.1.3. Core registers - Cortex-M3 Devices Generic User Guide

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0552a/CHDBIBGJ.html
kernel.c: replace interrupt number variable type from unsigned int to int

The later comparision compares interrupt number with a negtive number.
That means the variable should be a signed integer rather than unsigned
integer.
Update documentation/kernel-internal.md

Add ISR description and revise reference URL
Merge branch 'master' into proc_implement

Conflicts:
	Makefile
	kernel.c