Fixed the parsing of the block bitfield

Primarily I fixed an error that jjaquinta pointed out having to do with the bitfield used in the block data.

I also pulled out the entity parsing code from the meta file reader so it can be used to parse entity files in general.

Lastly added a check for the header byte in meta.smbpm file to be 0x3.  In the Isanth default blueprint this byte is a 0x1 and marked the end of the file.