AEPs and child comp feature addition in sl and vkernel using sl for scheduling

This is a follow up PR for PR #268 . Updates:

adds cos_sched_asnd with timeout and sched_tok parameters, mainly used in scheduling child component threads. (TODO: I think we need 2 different API for scheduling and normal ASNDs, which is how I've implemented here. But I wonder if cos_asnd should continue to take yield parameter with that design in mind. In my opinion, we don't need that parameters, we should let TCaps decide for normal ASNDs.)

Choose one (Mandatory):

[ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
[x] This PR is mature, and ready to be integrated into the repo.

@gparmer

As part of this pull request, I've considered the following:

[x] Comments adhere to the Style Guide (SG)
[x] Spacing adhere's to the SG
[x] Naming adhere's to the SG
[x] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
[ ] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions) No. When I run the format.sh on my PC, it seem to change every file to use 2 spaces for indentation, there could be something else too but I didn't look at the changes thoroughly. I believe there is more work required in that formatting tool with respect to different OSes. (I used clang-format-3.9 in my env).

[x] I've made an attempt to remove all redundant code
[x] I've considered ways in which my changes might impact existing code, and cleaned it up
[x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
[x] I've commented appropriately where code is tricky
[x] I agree that there is no "throw-away" code, and that code in this PR is of high quality

I've tested the code using the following test programs (provide list here):

gwsystems / composite