Add additional logging levels using a sub-classed logger

[DaveStrickland]

The standard python logger comes with the following named log levels: NOTSET, DEBUG, INFO, WARNING, ERROR, CRITICAL. In practice this limits logging of nominal processing to two levels: DEBUG and INFO, with occasional WARNING messages.

This flattened hierarchy results in large numbers of logged events having the same level and obscures the processing flow when operating on large numbers of files. The Boost logging library has a addition level below DEBUG called TRACE which is useful for tracing program execution at a lower level than DEBUG.

Sub-class the python logging class in AstroPhotography.core.logger to add new named levels:

• TRACE at a level below DEBUG
• OVERVIEW at a level above INFO but below WARNING

The new logging class should support named member function calls of the form logger.trace(msg: str) and logger.overview(msg: str)