Implemented BufferPool

Added try/catch block to handle exceptions
HeapPageId (Partial)

Only need to implement "equals" function. Will continue working later.
Implemented HeapPageId

Completed and passes tests
Implemented RecordId

Completed and passes tests
Merge branch 'master' of https://github.com/akhahaha/simpleDB

Conflicts:
	src/java/simpledb/BufferPool.java