Add encoding support.

[jheer]

• Add tableToIPC to encode a table as IPC bytes. Supports both the stream and file IPC formats and all data types.
• Add tableFromArrays and columnFromArray to encode JS data into a Flechette arrow table. Supports both explicit and inferred types, and fast paths for typed array data. Supports all data types except for "view" types.
• Add data type methods (int8, float64, dateDay, etc.) to create type instances.
• Add tableFromColumns method to create a table from existing Flechette columns.
• Add useDecimalBigInt conversion flag to support lossless access to decimal data as unscaled big integers. While the default still (lossily) maps decimal types to number, using bigint allows direct manipulation (addition, subtraction, etc) of decimal values, so long as they all share the same scale (number of fractional digits).
• Add column builder performance benchmarks, overall performance beats both Arrow-JS and JSON.stringify.
• Export Table, Column and Batch classes.
• Export batchType lookup method.
• Update internal decimal type handling, use BigUint64Array and bigint operations to encode/decode data.
• Update tests to cover new methods.
• Refactor internal data type and batch lookup by type id.
• Refactor dictionary batch initialization, allows batch completion prior to full dictionary completion.
• Add library documentation pages.

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