Add more primitive types of different sizes.

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Basil currently only supports word-size types, and has a small list of primitives: int, bool, symbol, and string. Since Basil is working towards being a viable systems-programming language, it would probably be best to support a variety of other common primitives, including:

• 8, 16, and 32-bit signed integer types.

• 32 and 64-bit floating point numbers.

• raw pointers.

Type coercion between some of these types would be useful, but not entirely necessary for the 0.2 update. We can revisit it later.

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Splitting this into several successor issues:

• Add floating-point primitives. #28 Floats and doubles are included as primitives in the new rewrite, so they'll be included in 1.0.
• Add sub-64-bit integer types as primitives. #29 Varying integer sizes are a little less essential...tentatively scheduling these for 1.1, but they may be moved into 1.0 if it's not too difficult.
• Add raw pointers and pointer types. #30 Raw pointer types are maybe the least essential. Scheduling these for 1.1, but we could stand to push these back further.