[WIP] Add failing specs for negative numbers and decimals.
Update implementation to support numbers without a leading integer.
[WIP] Fix specs for negative numbers.
Add spec for subtraction without spaces.
[WIP] Add specs for negative floating point numbers.
[WIP] Negative floating point numbers.
Fix implementation for negative floating point numbers.
* Fixes #11
* Fixes the-gss/engine#80
Add specs for positive signed numbers.
Use negative numbers directly instead of via an expression.
Merge pull request #20 from the-gss/negative-numbers-and-decimals

Signed numbers and decimals