gbx: Added basic mmap testing
docs: Design-doc stub
docs: Use simple README for docs

Current status of funex github-pages docs is not suffecient for
end users.

Signed-off-by: Shachar Sharon <shachars@xxxxxx>
Changed default blk-size to 4k

v0.1.2

Signed-off-by: Shachar Sharon <shachars@xxxxxx>