Added section about file system

Hey!

Today we have added new section about file system!
It has new articles. Here is the list of pages:
Read file in .net (c# / vb)
Write file in .net (c# / vb)
Encrypt file in .net (c# / vb)
Decrypt file in .net (c# / vb)
Open file in .net (c# / vb)
Check exists file in .net (c# / vb)
Delete file in .net (c# / vb)
Move file in .net (c# / vb)
Replace file in .net (c# / vb)
Copy file in .net (c# / vb)
Create file in .net (c# / vb)