Introduce a result interface to allow extraction of diagnostics

[ruediste]

I need access to the individual diagnostics messages. Unfortunately, the only implemented behaviour was to throw an exception when on compile errors/warnings. What do you think?

[codecov-io]

Codecov Report

Merging #19 into master will decrease coverage by 0.04%.
The diff coverage is 93.93%.

@@ Coverage Diff @@## master #19 +/- ##
=======================================
- Coverage 86.04% 86% -0.05% 
=======================================
Files 6 6 Lines 86 100 +14 Branches 8 10 +2 =======================================
+ Hits 74 86 +12 - Misses 10 12 +2 
Partials 2 2

Impacted Files	Coverage Δ
...n/java/org/mdkt/compiler/InMemoryJavaCompiler.java	85.71% <93.93%> (ø)	⬆️

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