v2.0.0

Changelog

• Custom variable name for sum/prod, eg. sum(k=1, 10, k) (breaking change)
• Vectors and matrices
• Functions that take vectors: min, max, average, perms, sort,
  length
• Vector comprehensions (experimental)
• Logical and/or/not
• true/false keywords
• mod keyword
• Nested sums and integrals
• Allow piecewise without 'otherwise' branch
• Show estimated fractions when displaying results
• Error handling for built-in functions and operations
• Numerical equation solving using Newton's method
• Result formatted with spaces, eg. 100 000
• Slightly improved formatting of results when using the --precision flag

...and more