Add support for negative numbers

Author: sd0e

.gitignore

@@ -0,0 +1 @@
+/node_modules

README.md

@@ -6,8 +6,8 @@ A JavaScript library which parses an equation in string format to a number.
 
 Current abilities:
 * Evaluate mathematical expressions with the following operators: `^`, `*`, `/`, `+`, `-`
-* Evaluate mathematical expressions with the following operators containing a number inside the brackets: `sqrt()`
+* Evaluate mathematical expressions with the following operators containing a number inside the brackets, with **trigonometric values represented in radians**: `sqrt()`, `sin()`, `cos()`, `tan()`
 * Evaluate mathematical expressions with brackets
-* Evaluate mathematical expressions containing multi-digit integers and floats
+* Evaluate mathematical expressions containing multi-digit positive and negative integers and floats
 
 Again, this library has not been fully tested so may not work as expected with these abilities.