v0.1.0

First public release of litfetch.

Resolve a scholarly-article identifier (DOI, PMID, PMCID) to its retrievable files and the markdown derived from them.

• Source ladder: PMC OA, bioRxiv/medRxiv, Unpaywall, Springer OA/Meta, Elsevier.
• Identifier resolvers (NCBI ID converter, Crossref, Semantic Scholar) and preprint <-> published relation lookup.
• Async Session facade with per-host pacing, retry with backoff, and a scoped response cache; injectable client_factory for institutional access.
• Typed, no baked-in contact identity: set Session(contact=...) for polite-pool access.