Update compounds.yml

Corrected teaspoon concentrations to accurately reflect the fact that volume = mass/density. That means 1tsp (5mL for simplicity) needs to be multiplied by the density to get grams, then must be multiplied by 1000 for milligrams. Simple stuff.

Prior to these changes, concentrations were off by roughly half which caused the calculator to recommend adding twice as much of each fert as necessary. This would result in vast over-fertilization and probably some serious algae issues.

I'd love to do the rest of the calculations, but I'm unable as I have no idea what the proprietary formulae contain and I don't understand some of the notation (I never was a big chem guy). This at least covers the macros.
Merge pull request #36 from cosalich/patch-1

Update compounds.yml