Update 3.5.md
Update 3.5.md
Create lex.l

Section 3.5
Update lex.l
Section 3.5
Section 3.5

Exercises from section 3.5
Section 3.5

Exercises from section 3.5
Section 3.5

Exercises from section 3.5
Update 3.5.md
Update 3.5.md
Rename lex.l to ..lex.l
Rename src/..lex.l to ch03/3.5/src/lex.l
Update 3.5.md
Exercise 3.5.1
Exercise 3.5.4
Update lex2.l
Update 3.5.md
Exercise 3.5.4
Exercise 3.5.4
Exercise 3.5.5