change syntax for default options
README.md typo fixes
Merge pull request #1 from go-oleg/patch-1

README.md typo fixes
raise exception when required option is undefined
resolve conflicts
small tweaks to tests, fix required option undefined logic
add clone for default value
fix readme
fix readme
fix readme
fix readme
fix readme
fix readme
fix readme
fix readme
add compatibility to readme
readme fix
readme fix
readme fix
readme fix