File change by part without load file on memory

[webdesus]

Some files can be bigger but we want to change only one little part of this file. Will be a stupid load all full file data in a memory.
It's will be interesting for people who work on own format.
I want to make two operations at the current moment:

• change_block. This operation will change only one information block
• change_blocks. This function will get many blocks for changes and will be made it more optimize
• Optimize change_blocks function.
• Write docs for both functions