79. convert snake_case to camelCase

Do you prefer snake_case or camelCase ?

Anyway, please create a function to convert snake_case to camcelCase.

snakeToCamel('snake_case') 
// 'snakeCase'
snakeToCamel('is_flag_on') 
// 'isFlagOn'
snakeToCamel('is_IOS_or_Android') 
// 'isIOSOrAndroid'
snakeToCamel('_first_underscore') 
// '_firstUnderscore'
snakeToCamel('last_underscore_') 
// 'lastUnderscore_'
snakeToCamel('_double__underscore_') 
// '_double__underscore_'

contiguous underscore __, leading underscore _a, and trailing underscors a_ should be kept untouched.