Update README.md

add (mainly) GitHub Flavored Markdown syntax highlighting

see https://help.github.com/articles/github-flavored-markdown/#syntax-highlighting
Merge pull request #11 from xuchunyang/trivial-fix

Update README.md
Replace Ruby with the native NASM macro

Note, the macro name, 'prologue', in 'src/kern/entry.S' is meaningless,
it is borrowed from nasm manual.
Merge pull request #12 from xuchunyang/patch-1

Replace Ruby with the native NASM macro
Makefile: build bootloader
Makefile: build kernel

All the middle objects files are exactly under the same path as source
files, instead of move they to ./bin

Beside, since 'tool/main.ld' is changed, 'Rakefile' should
not work as we excepte.
Merge branch 'wip/makefile' of https://github.com/xuchunyang/fleurix into wip/makefile