Resolve #260 Introduce GeneratorConfig

[tefra]

Introduce a generator configuration with more options like custom naming schemes and aliases.

https://xsdata.readthedocs.io/en/issue-260/codegen.html#configuration

<?xml version='1.0' encoding='UTF-8'?>
<Config xmlns="http://pypi.org/project/xsdata" version="20.9">
  <Output wsdl="false">
    <Package>generated</Package>
    <Format>pydata</Format>
    <Structure>filenames</Structure>
  </Output>
  <Conventions>
    <ClassName case="pascalCase" safePrefix="type"/>
    <FieldName case="snakeCase" safePrefix="value"/>
    <ModuleName case="snakeCase" safePrefix="mod"/>
    <PackageName case="snakeCase" safePrefix="pkg"/>
  </Conventions>
  <Aliases>
    <ClassName source="fooType" target="Foo"/>
    <ClassName source="ABCSomething" target="ABCSomething"/>
    <FieldName source="ChangeofGauge" target="change_of_gauge"/>
    <PackageName source="http://www.w3.org/1999/xhtml" target="xtml"/>
    <ModuleName source="2010.1" target="2020a"/>
  </Aliases>
</Config>

[codecov]

Codecov Report

Merging #265 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #265    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           66        66            
  Lines         4819      5039   +220     
  Branches       825       862    +37     
==========================================
+ Hits          4819      5039   +220     

Impacted Files	Coverage Δ
xsdata/codegen/handlers/class_extension.py	100.00% <ø> (ø)
xsdata/formats/dataclass/utils.py	100.00% <ø> (ø)
xsdata/cli.py	100.00% <100.00%> (ø)
xsdata/codegen/handlers/attribute_mismatch.py	100.00% <100.00%> (ø)
xsdata/codegen/mappers/definitions.py	100.00% <100.00%> (ø)
xsdata/codegen/mappers/schema.py	100.00% <100.00%> (ø)
xsdata/codegen/models.py	100.00% <100.00%> (ø)
xsdata/codegen/resolver.py	100.00% <100.00%> (ø)
xsdata/codegen/sanitizer.py	100.00% <100.00%> (ø)
xsdata/codegen/transformer.py	100.00% <100.00%> (ø)
... and 20 more

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