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Removed BigInteger dependency.

• Upgraded to new BigInteger version

• Typehinting

• Introduce a Hash class

• Using intervention/image to support both GD and ImageMagick

• Fix hexadecimal to decimal conversion for negative hashes

• Added hashFromString method

• Introduce ImageHash:HEXADECIMAL and ImageHash:DECIMAL mode

• Return hexadecimal values instead of integers. Warning: this breaks backwards compatibility!

• Fixed issue with hamming distance calculating and the GMP extension.