Whitespace.
Allow access to the additional columns that were found.
Whitespace.
Rename "ignore_extra_columns" to "allow_extra_columns".

We're not just ignoring them any more!
spelling: preceed* => preced*
Create add_ methods for links to profile items and subject mappings.
Add support for setting tags when creating subject mappings.
Consolidate get() attempts to single statement.
Revise file_path doc text for correctness.
Remove unused include.
Test that the correct columns are "extra".
Merge pull request #36 from tmooney/tag_somval_subject_mappings

Allow Tags in Subject Mapping Importer for Somatic Validation