Namespace Functions, Constant Retry & Logging

[hughsaunders]

• To prevent collisions with built-ins and user functions, all bash-lib functions now have the prefix bl_. This is a major breaking change and will be released as v2.0.0
• Conditional logging functions based on BASH_LIB_LOG_LEVEL with appropriate colouring for each level.
• retry_constant function, similar to retry but with a retry_constant interval between attempts.