Brown University is kicking off a 15-month-long celebration for its 250th anniversary. The school was chartered in 1764 and opened its doors as the College of Rhode Island in Warren in 1765. It was the third college in New England, after Harvard and Yale, and was the only Ivy League university to allow students of all religions to attend. The college was renamed in 1804 following a $5,000 gift from Providence businessman Nicholas Brown. Brown’s celebration started Friday with a lecture by World Bank president Jim Yong Kim. Saturday will feature a colloquium convened by Brown president Christina Paxson on the virtues of a liberal education.