Added custom mob head: pig zombie (Thanks cnaude of TrophyHeads)
Verifying strings only works if both of them are lowercase
Converted to Maven
Converted from tabs to spaces, removed all unnessicary whitespace
Updated default drop rates
Added custom mob heads: snowman, and ghast (Thanks MrLeikermoser)
Added custom mob head: pig (Thanks XlexerX)
Added missing license info at the top of code files