* added yaml/style that defines representation pragmas
`scalar` and `collection`
* implemented those pragmas
* updated docs. also fixes some invalid links in docs
* moved load procs to yaml/loading.nim
* moved input YamlStream into ConstructionContext
* made ConstructionContext a non-ref object
* harmonized code style & comments
* renamed yaml/serialization.nim to yaml/native.nim
* removed default value objects,
use Nim2 default vaules for fields instead.
* moved dump procs to yaml/dumping and introduced Dumper
* modified serialization procs to use ctx as first argument,
so that prefix calls can be used
* changed defaults for presentation to be more like other
YAML implementations, e.g. no directives by default.
* Removed deprecated procs in DOM API
* Removed PresentationStyle – use the setXStyle procs of Dumper
instead.
* Fixed some warnings emerging from transitioning to Nim2
* PresentationOptions has gained more fine-tuning options:
* directivesEnd: specifies when `---` is written. ref #135
* containers: specifies whether containers use block or flow style
* suppressAddrs: if set, suppresses output of attributes
* quoting: specifies how strings should be quoted
* condenseFlow: specifies whether flow sequences should be on a
single line
* explicitKeys: specifies whether mapping keys should always have '?'
* PresentationStyle is now a list of presets that set
multiple options in PresentationOptions.
* Does not output trailing spaces anymore. ref #135
* Writes compact notation, i.e. a mapping in a sequence starts on the
line with the sequence's `-`, unless attributes are written
* Added tests for the presenter
* Existing code might change behavior because of whitespace, `---` and
compact notation. The API has been extended so that existing code is
affected as little as possible.
