Avoid synthetic constructors by default

[pettermahlen]

This PR does two things:

• changes the behaviour of DataEnum to by default generate package-private constructors, to avoid synthetic constructors being created by the compiler.
• adds the ability to configure which access level is desired on a per-package basis. This is unlikely to be used very often, but may be useful for purists that want to ensure the static factory methods are used to create cases, not the constructors.

[togi]

I think it'd be good to include a note in the readme about this feature and its default configuration. And on a separate not It would be nice if we could set up an integration test to check for synthetic methods, eg using https://github.com/JakeWharton/dex-method-list

[codecov-io]

Codecov Report

Merging #14 into master will decrease coverage by 1.23%. The diff coverage is 81.81%.

@@             Coverage Diff              @@
##             master      #14      +/-   ##
============================================
- Coverage     94.78%   93.55%   -1.24%     
- Complexity      179      192      +13     
============================================
  Files            21       23       +2     
  Lines           556      605      +49     
  Branches         80       83       +3     
============================================
+ Hits            527      566      +39     
- Misses           22       30       +8     
- Partials          7        9       +2

Impacted Files	Coverage Δ	Complexity Δ
...num/src/main/java/com/spotify/dataenum/Access.java	0% <0%> (ø)	0 <0> (?)
...potify/dataenum/processor/parser/ValuesParser.java	94.11% <100%> (ø)	5 <0> (ø)	:arrow_down:
...com/spotify/dataenum/processor/util/Iterables.java	94.11% <100%> (+0.36%)	10 <1> (+1)	:arrow_up:
...um/processor/generator/value/ValueTypeFactory.java	98.05% <100%> (ø)	42 <4> (ø)	:arrow_down:
.../spotify/dataenum/processor/DataEnumProcessor.java	92.85% <100%> (+0.75%)	17 <0> (ø)	:arrow_down:
...enum/processor/generator/spec/SpecTypeFactory.java	97.22% <100%> (+0.34%)	3 <0> (ø)	:arrow_down:
...com/spotify/dataenum/processor/AccessSelector.java	85.71% <85.71%> (ø)	12 <12> (?)

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[pettermahlen]

README docs added - about an integration test, I think it would be better to use something that looks at the actual modifiers, looking for SYNTHETIC (see for instance http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/lang/reflect/Modifier.java#Modifier.0SYNTHETIC) - it's 'secret', but that should anyway be safer than checking for a particular kind of method names to identify synthetic methods (cf the synthetic constructor names listed in #13). But that's for some other PR, I'd say. :)