store pages according to the following format (Tianwang format):
1) a raw page depot consists of records, every record includes a raw data of a page,
records are stored sequentially, without delimitation between records.
2) a record consists of a header(HEAD), a data(DATA) and a line feed ('\n'), such as is HEAD + blank line + DATA + '\n'
3) a header consists of some properties. Each property is a non blank line. Blank line is forbidden in the header.
4) a property consists of a name and a value, with delimitation ":".
5) the first property of the header must be the version property, such as: version: 1.0
6) the last property of the header must be the length property, such as: length: 1800
7) for the sake of simplicity, all names of properties should be in lowercase.
Example: (tip: codes to generate the following lines)