revise chapter 1 :uk:
revise :uk: 2.1 2.2
add draft translation for section 2.1
translate map, fold and filter of chapter 02
capitalize TOC of section 2.1, 2.2
revise chapter 1 :uk:
update translation of high order function of chapter 02
update README of chapter 02, the higher-order function
translate more on README.md of chapter 02
translate currying of chapter 02
revise :uk: 2.1 2.2
merge and revise
Merge pull request #4 from jcouyang/en-version

update revised English version from jcouyang's repo, part of chapter 02