Yet another file system mock library in go

Features:

• performance in non mock path (no interfaces)
• profound testing (we use property based tsting to ensure simularity with real implementation)

Non features:

• make a variety of different backends (NetFS, google cloud, s3, etc.). I try to keep this package as clean from dependencies as possible
• simulating of concurrent effect of filesystem (e.g. concurrent ReadDir with file removing in different goroutine)

TODO:

• Document what fileMode are supported
• O_APPEND
• Fallocate?
• copy paste docs from orig functions
• add mode there instead on std error we get stacktrace inside error?
• add thread safe fs?
• add benchmark to track allocation
• make good readme file
• try to add fuzzing (and try to introduce errors)
• add example of extension (compressed reader?)