Merge pull request #5 from jcouyang/en-version

update revised draft from jcouyang's repo
capitalize table of content for chapter 02
translate chapter 03 pattern matching
start to translate chapter 04 functor and monad
add draft translation of functor in chapter 04
merge 2nd part of functor translation
finish functor draft translation
finish draft translation of monad
remove Chinese sentences in markdown files of chapter 04
translate "monad in js" of chapter 04
update monad in js of chapter 04
revise functor
revise monad