fixes #908: use strsplit() instead of str_split(), since the regex syntax has changed in stringr, which uses ICU regex now
changes due to a new feature of klutometis/roxygen#291
the new version of stringr has deprecated perl()
turn NA matches to empty strings, e.g. parse_inline('And you know the value of pi is +r pi+.', all_patterns$asciidoc) will return NApi, which is wrong; the reason for that is the pattern all_patterns$asciidoc$inline.code is  "`r +([^`]+)\\s*`|[+]r +([^+]+)\\s*[+]", and | produced the NA; the example 089 will fail without this fix
tweaks after #903

- always use knit_global() (unless someone really asks for a custom environment)
- do not use make.names(), otherwise it might be confusing (what I provided is not what I get)
a news item for #903
roxygenize after #909
bump version