rgsrs 0.1.0

New functions

• gsrs_search(): free-text and Lucene-syntax search across GSRS substances, with optional automatic pagination.
• gsrs_substance(): fetch substance metadata by UNII (vectorized).
• gsrs_names(): retrieve all registered names / synonyms for one or more UNIIs.
• gsrs_codes(): retrieve all cross-reference codes (CAS, PubChem, ChEMBL, WHO-ATC, DrugBank, etc.) for one or more UNIIs, with optional code_system filter.
• gsrs_unii_from_name(): resolve substance names to their UNII identifiers.
• gsrs_structure(): fetch chemical structure data (SMILES, formula, MW, InChI, stereo info) by UNII.
• gsrs_structure_search(): substructure, similarity, exact, and flexible structure search by SMILES.
• gsrs_chem_info(): retrieve chemical structure information from any identifier — name, CAS, UNII, InChIKey, or SMILES.
• gsrs_hierarchy(): retrieve the parent/child relationship tree for a substance.
• gsrs_browse(): page through the full GSRS substance catalogue.
• gsrs_vocabularies(): retrieve all controlled vocabulary terms.
• gsrs_all(): convenience umbrella returning substance metadata, names, codes, structure, and hierarchy in a single named list.
• write_dataframes_to_excel(): write a named list of data frames to an Excel workbook (requires openxlsx).