Negative numbers were handled properly in math expression

[MarinaRybalko]

Current implementation doesn't work properly with negative numbers.
I've added logic to handle negative numbers properly.

Here I added expressions I tested my implementation on.

Expression "-123" fails with following exception

Exception in thread "main" java.lang.RuntimeException: Unexpected token: - at position: 1
	at ru.arhiser.parser.Main.factor(Main.java:204)
	at ru.arhiser.parser.Main.multdiv(Main.java:166)
	at ru.arhiser.parser.Main.plusminus(Main.java:144)
	at ru.arhiser.parser.Main.expr(Main.java:139)
	at ru.arhiser.parser.Main.main(Main.java:24)

Expression "(1 - 2) + -(-(-(-4)))" fails with following exception

Exception in thread "main" java.lang.RuntimeException: Unexpected token: - at position: 7
	at ru.arhiser.parser.Main.factor(Main.java:204)
	at ru.arhiser.parser.Main.multdiv(Main.java:166)
	at ru.arhiser.parser.Main.plusminus(Main.java:149)
	at ru.arhiser.parser.Main.expr(Main.java:139)
	at ru.arhiser.parser.Main.main(Main.java:24)

Expression "12* 123/-(-5 + 2)" fails with following exception

Exception in thread "main" java.lang.RuntimeException: Unexpected token: - at position: 5
	at ru.arhiser.parser.Main.factor(Main.java:204)
	at ru.arhiser.parser.Main.multdiv(Main.java:174)
	at ru.arhiser.parser.Main.plusminus(Main.java:144)
	at ru.arhiser.parser.Main.expr(Main.java:139)
	at ru.arhiser.parser.Main.main(Main.java:24)

Expression "12 * -123" fails with following exception

Exception in thread "main" java.lang.RuntimeException: Unexpected token: - at position: 3
	at ru.arhiser.parser.Main.factor(Main.java:204)
	at ru.arhiser.parser.Main.multdiv(Main.java:171)
	at ru.arhiser.parser.Main.plusminus(Main.java:144)
	at ru.arhiser.parser.Main.expr(Main.java:139)
	at ru.arhiser.parser.Main.main(Main.java:24)