<issue_start><issue_comment>Title: Remove dependency on OE heap
username_0: This PR adds an allocator (dlmalloc) to the Mystikos kernel and removes the dependency on the OE heap. This eliminates fragmentation caused by splitting the memory space into **user-memory** and **kernel-memory**.

This change cuts the kernel boot time by three.
<issue_comment>username_1: https://github.com/deislabs/mystikos/issues/193
<issue_comment>username_0: I'm looking for a better option name than --ram=<size>. What about --heap-size=<size>?
<issue_comment>username_1: The memory is used for both stack and heap of user threads (pthreads). How about `--memory-size`?
<issue_comment>username_0: perfect!
<issue_comment>username_1: Thanks for the optimization. Looks great!