"Jane Roe’s complaint, originally filed in March 1970, states that she was pregnant and that she was unable to obtain a legal abortion in Texas because of Texas’s abortion statute. From these facts there is no doubt that she possessed standing to challenge the statute even though Texas’s criminal prohibition is directed at those who perform abortions, rather than at the women who receive them, for the law effectively prevents her from obtaining a legal abortion in Texas. Texas, however, argues that since neither Roe nor anyone in the class she represents is now pregnant, her case is moot."