Owmeta-core

Fixes
-----
- Updating HTTPBundleLoader's can_load method for the new index format

Features and Enhancements
-------------------------
- Changing init_rdf_type_object deferral mechanism to be based on a
property. Makes initialization more explicit and predicatable, and
it allows for the same mechanism to work for modules outside of
owmeta_core.dataobject

Also, adding augment_rdf_type_object hook into init_rdf_type_object
so so there's less boilerplate for augmenting the default
rdf_type_object
- Adding hash verification to HTTPBundleLoader. Breaks the previous
format for index files since I want to require bundle hashes
- Adding `context` option to `owm` so all sub-commands can rely on that
rather defining their `context` options
- Removing `imports_context_id` from from `OWM.init`: it was not being
used anyway.
- Defined `context_carries` property for carrying values through class
contextualizations

Fixes
-----
- Fixing `ContainerMembershipProperty` default link
- Removing `Property` default link (never made sense)
- Updating `base_namespace` and `base_data_namespace` on `Property` and
defining

Features and enhancements:
- Added a command, `owm contexts list-importers` to list contexts which
import a given context
- Added a default value for `lazy` on `dataobject_property.Property`
sub-classes so they need not be defined every time.

Fixes:
- Fixed formatting exception messages in `OWM.translate` for
DataTranslator and DataSource arguments (rather than identifiers)

Misc:
- Updated some documentation

To better capture the purpose of owmeta, the project was renamed from
"PyOpenWorm" to "owmeta" and then owmeta was split into owmeta and owmeta-core
(this library). Also, the yarom library, which provided some PyOpenWorm
features, was also merged back into owmeta-core

Features and enhancements:
- Dropped module import recording
- Removed requirement to declare classes manually in `__yarom_mapped_classes__`
- Added support for RDF Bag, Alt, Seq, List collection types
- Created distinct base namespaces for DataObject sub-class instances and
properties
- Added support for dependencies on bundles in projects
- Added sub-commands for retracting statements from a project:
- Removing Context imports
- Removing DataTranslator
- Removing DataSource
- Removing classes
- Removing RegistryEntry
- Removing all statements in a context
- Added a sub-command for listing RegistryEntry objects
- Started defining dataobject.Property classes from Informational during
DataSource class definition
- Added a sub-command for listing derived DataSources from a given DataSource
- Completed basic bundle features (install, fetch, deploy, save to file, RDFLib
query)
- Added an alternative way to do queries that batches queries of a common type
for faster execution

Internal/Misc. changes:
- Removed identifier-based equality for DataObject instances
- Dropped Python 2.7 support
- Added 3.8 support
- Switched to the new Github issue template format
- Started triggering downstream builds in Travis-CI
- Dropped several unused dependencies
- Replaced numpydoc for faster parsing of OWM docstrings
- Fixed preservation of leading whitespace in `owm diff` output lines

Known Issues:
- Not all operations `owm` sub-commands are fully supported with a SQL DB
source (due to incomplete support for Dataset/graph-aware semantics)