Benchmarks for XLSX library

Some benchmarks for https://github.com/plandem/xlsx and other XLSX libraries in GO

It was not a goal to make best of the best, but the same time it's interesting to know pros/cons. For some cases this library is second, for other - best, but in case of reading huge files - the only.

• ! - does not mutate information directly, so faster get/set, but slower read/write files - sometimes it can take forever to open file.
• !! - corrupted file after saving, lost styles/formatting

Benchmarks report