added schema file globbing fixes #631

[cbelsole]

Describe your PR and link to any relevant issues:

This fixes #631 by implementing globbing for schema files.

Tested with:

# schema:
# - schema/schema.graphql
# - schema/models/todo/todo.graphql
# - schema/models/user/user with spaces.graphql

# schema:
# - schema/schema.graphql
# - schema/models/user/*.graphql
# - schema/models/todo/*.graphql

# schema:
# - schema/schema.graphql
# - schema/**/user/*.graphql
# - schema/**/todo/*.graphql

# schema:
# - schema/schema.graphql
# - schema/models/**/todo.graphql
# - schema/models/**/user with spaces.graphql

# schema:
# - schema/schema.graphql
# - schema/models/**/*.graphql

# schema:
# - schema/**/*.graphql

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[cbelsole]

@vektah any interest in merging this?

[mathewbyrne]

Thanks for the contribution!