FIFO Generator updates and improvements

[sarmadsalman-RS]

This Pull Request contains the following updates:

• BRAM Usage optimization by utilizing FIFO18KX2, saving up to 25% resources
• Updated FIFO36K and FIFO18KX2 primitives according to new spec from George
• Added pointer logic for designs with data_width <= 36 and depth <= 1024 as a workaround for the hard FIFO full and empty signal limitations
• Laid the foundation for asymmetric accesses in the FIFO.v, FIFO18KX2.v and FIFO36K.v wrappers.
• Updated README.md