Added expressions for the body of assignements

...es/nperier/minichamo/language/expressions/Expression.java

...r/minichamo/language/expressions/base/BaseExpression.java

...r/minichamo/language/expressions/base/BoolExpression.java

...r/minichamo/language/expressions/base/CharExpression.java

.../minichamo/language/expressions/base/FloatExpression.java

...er/minichamo/language/expressions/base/IntExpression.java

...minichamo/language/expressions/base/StringExpression.java

...r/minichamo/language/expressions/base/UnitExpression.java

...insarennes/nperier/minichamo/lexing/tokens/BoolToken.java

...nsarennes/nperier/minichamo/parsing/ExpressionParser.java

...ennes/nperier/minichamo/parsing/ExpressionParserTest.java