Implement and enforce requirements for names of attributes, resolvers, and matchers.

[davemoore-]

Attributes, resolvers, and matchers should have the same naming requirements as entity type names (see #58) for the same reasons listed in that issue.

This change should be included in the same release as #58 so that users can fix deprecated names in their entity models in one release.

Index names and index field names can be excluded from this validation. Elasticsearch validates those, but only zentity can validate attributes, resolvers, and matchers.

[davemoore-]

Opened PR #75

[davemoore-]

Merged