standard input and output for Bioconductor packages

 Implements `import()` and `export()` standard generics
 for importing and exporting biological data formats. `import()`
 supports whole-file as well as chunk-wise iterative import. The
 `import()` interface optionally provides a standard mechanism for
 'lazy' access via `filter()` (on row or element-like components of
 the file resource), `select()` (on column-like components of the
 file resource) and `collect()`. The `import()` interface
 optionally provides transparent access to remote (e.g. via https)
 as well as local access. Developers can register a file extension,
 e.g., `.loom` for dispatch from character-based URIs to specific
 `import()` / `export()` methods based on classes representing file
 types, e.g., `LoomFile()`.