Changes:

• Fix write time complexity being quadratic: Write to a rope rather than recursively concatenating strings; fixes Encoding runs in worst-case quadratic time #45
• Fix number encoding: For 64-bit floats, up to 17 digits must be written; presumably fixes Large numbers serialized incorrectly #41
• Fix benchmarks: Do GC before benchmarking to not drag down implementations that run later, inheriting the garbage of previous implementations. Also, bump up the runs by 10x because otherwise the variance is simply too large.
• Fix tests: Using full double precision unfortunately means unclean numbers pop up.
• Optimize string parsing: Use a rope for string parsing to bring it back down to linear time complexity (also leads to less garbage); fixes There is an idea to optimize the code for json.lua #34

Choices involved:

• A rope is passed to all write functions. Alternatively, a "write" function could be passed; that would incur function call overhead however, in exchange for making the code slightly more readable.
• rope[#rope + 1] is preferred over table.insert due to better performance on PUC Lua.
• The rope parameter could be gotten rid of by using closures for all write functions instead and making the rope / write function an upvalue.