emld 0.5.0

User-facing changes:

Rewrote logic around how emld works with schemaLocation:
- The schemaLocation argument on as_xml used to fill in a default value that pointed to a local copy of eml.xsd. Now, it automatically fills in a web-resolvable location to make validating documents easier out of the box.
See #44 & #45.
Re-worked the logic for handling schemaLocation when serializing to XML:
- When schemaLocation is present on the emld object, it is used verbatim (no change in API here) regardless of the schemaLocation argument of as_xml.
- When schemaLocation is absent on the emld object:
  - as_xml(..., schemaLocation = TRUE) causes a value to be guessed.
  - as_xml(..., schemaLocation = FALSE) explicitly prevents a value from being filled in when serialized.
  - as_xml(..., schemaLocation = "Some value) explicitly sets the provided value.
See #44 & #45.
emld::eml_validate no longer depends on schemaLocation to determine the correct XSD to use during schema validation and now uses two helpers (See below) to find the correct schema file. See #52 & #45.
emld::eml_version now allows specifying the version without the eml- prefix, like `eml_version(“2.1.1”), and will throw a warning when it gets output that doesn’t ’look right rather than silently failing.
Fixed a bug where the EML 2.1.1 units dictionary was being used for EML 2.2.0 docs which would cause spurious validation errors. See #56.

Developer-facing (non-exported) changes:

Added two new helper methods:
1. find_real_root_name(doc : xml_document) : list(prefix : character, name: character) which returns the namespace prefix and the local name of the root element on an xml_document.
2. guess_root_schema(doc : xml_document) : list(module : character, version : character, namespace : character) which returns the module, schema version, and namespace URI of the root element on an xml_document.
schemaLocation is now ignored during roundtrip testing because of the new (above) behavior of emld with respect to schemaLocation.
Roundtrip testing can now handle documents that are supposed to be invalid but still roundtripped. Specify intentionally invalid files by adding “invalid” (case insensitive) to the filename in inst/tests.

Other changes:

emld 0.4.0

Fixed serialization bug for references attributes #48
Fixed validation bug: packageId is now used as an identifier for checking uniqueness, and no more errors for annotation elements in additionalMetadata. #49
Fixed validation bug: XPath was referencing the element rather than the attribute references. #47

Updated package to support version 2.2.0 of EML. #40. See the EML website for more information on the 2.2.0 release.
Fixed a minor XML serialization issue with TextType nodes where extra whitespace was being added. #37.
Relaxed eml_validate’s behavior when validating custom units. #35.