Use unique identifier for individuals for user-based views

[astrochun]

Closes #60

Commit history:

• Add initial set_unique_identifier function
• Set unique_df with first dataframe
• Add write_file function
• Refactor to get_unique_names() function
• Add append_to_df function
• Add year column
• Add new unique records to unique_df
• append_to_df: Add year keyword option
• Define df_dict to later update with uid
• Sort unique_df by name and set uid
• Update each year with uid for unique_id matches
• Remove commented out code
• Use DataFrame.insert to fix pandas SettingWithCopyWarning warning
• Specify year with first append_to_df call for ii=0
• Add write_csv_with_uid function
• Add support to set output folder
• Refactor code with unique_match_id, non_unique_check
• Minor indent fix
• Bump version: v0.2.1 -> v0.3.0
• Update CHANGELOG.md for v0.3.0

[astrochun]

Changes look good.

Files were uploaded to Google Drive. This includes the unique.csv. Tested locally and no issue with data views, with each FY data.