* Call the HalfInteger field twofold
Makes it more immediately obvious what the meaning of the value stored
in the field is.
* Introduce new constructors for HalfInteger
The primary inner constructor mirrors the two-argument constructor of
the Rational type, where the user provides the numerator and denominator
values.
There is also a single argument outer constructor that makes HalfInteger
behave like a normal numeric type such that HalfInteger(n) == n.
* Move HalfInteger tests to a separate file
The using statements in halfinteger.jl are there so that it would be
possible to run the file separately from the other tests.
* Test the single-argument HalfInteger constructor
* Organize halfinteger.jl a bit
Prioritise the convert methods.
* Add multiplication with integer to HalfInteger
* Implement parsing and printing for HalfInteger
* parse(::HalfInteger, x) method
* Overload show to pretty-print HalfInteger
* Overload Base.numerator/denominator
And add tests for the other supplementary functions and methods as
well.
* Add HalfIntegerRange type
Can be constructed using the range operator :. Currently only supports
unit steps in the positive direction.
* Address feedback
* Rename .twofold -> .numerator
* Consistent variable names
* Remove unnecessary methods for HalfIntegerRange
* Allow constructing HalfIntegerRange with non-integer difference
* Add docs and ceil(::HalfInteger)
