Version 0.1.6

Changes in this version:

• Support parsing of numbers with recurring digits (e.g. 0.(3) is equal to 1/3)
• Support outputting mixed fractions (implicitly or via to mixed_fraction)
• Support unmatched parentheses (e.g. 2+3)*(1+2 is 15)
• Allow numbers that start with a decimal point, such as .1