Expose debug mode and use PSR logger

[mattfarina]

In a few places there is a debug mode that prints to standard out. We can expose this in the Html5 and use the PSR logger interface (still printing to standard out by default).

[goetas]

yay! :+1: nice ti have in 3.0!

[stof]

I think adding support for a PSR logger could even be done in 2.x in a BC way

[goetas]

hmm, can you explain your idea?

[stof]

Well, you could add support for injecting a logger (which would be optional):

• logger injected -> log stuff at debug level in the logger
• no logger injected and debug mode turned on -> write to stdout (and report that as deprecated during initialization ?)
• no logger injected and debug mode turned off -> no debug info

The remaining question is whether the logging itself should be subject to the debug mode or no. I don't think it is needed: injecting the logger would be optional, and then most logging library also provide a way to ignore log messages below a given level.

[stof]

hmm, it looks like the only usage of the debug mode is to dump the input string at the beginning of the processing. So maybe it is not even useful.

[goetas]

Also to me looks non that useful.

From what I can guess. Was used at the very beginning of the library, just for debug purposes