Bitmap functions

Implemented bitmap functions. The functions are:

• bitmap_bucket_number(): returns the bucket number for a given input number
• bitmap_bit_position(): returns bit position for a given input number
• bitmap_count(): returns the number of set bits from an input bitmap
• bitmap_construct_agg(): aggregation function that aggregates input bit positions, and creates a bitmap
• bitmap_or_agg(): aggregation function that performs a bitwise OR on all the input bitmaps