Massachusetts continued its long slog out of the recession in April, as employers added jobs for the fifth consecutive month and the state unemployment rate fell to its lowest level in more than three years. The jobless rate slipped from 6.5 percent in March to 6.3 percent last month, reaching its lowest level since October 2008, when the financial crisis was near its worst, the state’s Executive Office of Labor and Workforce Development reported Thursday. Massachusetts employers added 2,500 jobs last month after increasing payrolls by 7,500 jobs in March.