add transport scoped parameters for CompressedPublisher

[bmegli]

Fix for #140

This is #142 re-targeted at rolling

Changes

Compared to #142

• rolling supports runtime reconfiguration
• rolling has nested attributes (tiff.xdpi)

runtime reconfiguration

rolling supports runtime reconfiguration (reads params at the beginning of publish)

This forced us to synchronize deprecated values to correct ones. Otherwise deprecated values would not be used.

I purposefully synchronize only in deprecated -> non-deprecated direction.

nested attributes

Handler emitting deprecation warnings now handles nested attributes (like tiff.xdpi)

warnings

Now not emitted if new value was already set like deprecated one.

This will not emit warnings if somebody is using default values (not setting anything)

structure

All constants (parameter definition)

• were separated from logic
• and exist in constant compile time defined array
• parameters are declared automatically from this table

Next Steps

Again, this only targets compressed_publisher

If we agree on direction I can rework the rest along.

Refactoring

If generalizing for multiple transports:

• constant parameter array would be thrown to new file like compressed_publisher_cfg.h
• declareParameter may become free function shared by all transports
• onParameterEvent may become free function shared by all transports

In particular header and implementation would be further cleared from (common) parameter related code

[ijnek]

Thank you for your contribution of the refactoring and the great improvements!
I will make sure that these changes will be available in the upcoming iron release.