rcxl 0.1.2

Worker threads are now joined before an R error propagates. Previously an error while building text columns or parsing workbook metadata left them running and writing into freed memory, which could crash the session or corrupt data. A raw NUL byte in a cell was enough to trigger it.
An na marker stored XML-escaped in the sheet, such as N&A for "N&A", or split across the rich-text runs of an inline string, is now matched before the column type is guessed. Previously such a cell counted as text, so a numeric column holding it came back as character instead of numeric with an NA.
Documentation corrections. RCXL_THREADS overrides the 4 MB serial threshold rather than being bound by it, the architecture description no longer claims cells are decoded straight into R vectors, and the readxl comparison notes that na matches numeric cells by value.

rcxl 0.1.1

Fixed a compile failure on macOS with the macOS 11 SDK, whose stdio.h declares a BSD zopen() that collided with an internal helper of the same name. The helper family is now prefixed zsrc_.