1, Fix: File is being used by another process error on atomic write. Closed temporary file conditionally,

* added encryption support in fdb 
* added feature of dynamic encryption key generation function

* removed unused code
* added lock for reading pack file

moved packfile related functions in filemdl and done changes in fdb accordingly

1. Fix: Atomic file not updated, Hard link issue.
2. Add: Create temp directory if not present at app root.

const changed to var due to build issues on windows

FDB changes for reindex, filepack, fast read and write changes

added reindexing feature in fdb,
added filepack module,
modification in filemdl module

test cases added

added test cases

added zip and unzip methods

file is empty

test cases added for zip

Added test cases as needed

Added review comments