Angus Davis, founder and CEO of a fast-growing Providence technology company, said Thursday a $20-million venture-capital investment in his firm will allow Swipely to “accelerate growth” in the capital city by hiring more employees, attracting more customers and improving what it sells them. The company Davis founded in late 2009 employs more than 100 people and manages more than $2 billion in annual sales for merchants who use its system in more than 40 states. That’s up from $1 billion in sales it managed in November. Davis expects to have 200 employees by the end of 2015, he said. That’s a far cry from nearly 30 he employed at the start of last year.