Merge pull request #1 from helmedeiros/level-1

Level 1 - operators
Merge pull request #3 from helmedeiros/level-1

Level 1 - booleans
Add something about srtings
add concatanation
add numbers and expressions
explain backslash
string equal operator
String length property
String special characters challenge and answer
challenge with string comparison
string concatenating challenge
string properties challenge