First stable release!

Changelog

• The numeric_range library is now used under the hood. It improves lookup efficiency from linear to logarithmic, and also makes error-checking nicer to deal with.
• The calculate() function returns std::nullopt instead of throwing an std::runtime_error if an input value is not contained in any pieces' bounds. This necessitates using c++17's std::optional features.
• Adds a comprehensive testing suite.
• Bumps up json.hpp version.

2nd Alpha Release

More ideas in the pipeline (like tree traversal for equation evaluation!), but this should work as the current stable version.

First working alpha release

Builds a piecewise single-variable function from an input stream formatted in JSON. The calculate() function can then be used to find the result of plugging in an input value for the variable.
Next on the to-do is adding more helpful exception classes and their corresponding messages.