Links to used libraries using MD named references

[mgrojo]

Added bingada and protobuf as examples for gtkada and matreshka.

The reference link syntax has the following advantages:

• URLs only specified once
• Standard and easy link to used libraries in definitions, so people find examples for the library
• More readable if the syntax is promoted for all the links (this is subjective, anyway)

A future possibility would be to process the list to generate another file for listing dependents for each library having them, e.g. applications using [gtkada], using [matreshka], etc.

[mgrojo]

This was inspired by comments about difficulty finding examples, e.g. https://www.reddit.com/r/ada/comments/tbqs1g/lessons_learnt_moving_a_gtk_application_from_go/

[ohenley]

Super. Thx Manuel.