Log Message:
math/kalker: update to 2.0.0

   -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