Add single database connection functionality added, unit test,  example added for the same, and readme file changes done.

List users and list databases feature, Creating specified (hidden) directory while init connection and TestCbConnection bug fix.

1. If dir path is provided - checking folder exists and accessible for current user.
2. DefaultHostname var exported.
3. GetImmuDAOWithHost documentation changes.

Added readme.md file, Init connection, delete conn, get conn, and all read methods documentation added.

Added unit test for the same
Setting default limit in GetKeyHistory if limit value is not passed

CreateDatabase, DeleteDatabase, CreateUser functionality added for Immudb, and test cases for the same.

AddNewImmuDbConnection - method removed