lib/file: document and fix `file_extension`

Also remove the redundant (thus useless) test file.

Fixes #160
Signed-off-by: Jean Privat <jean@pryen.org>
lib/file: more documentation and nitunit tests

Fixes #160
Fixes #161
Signed-off-by: Jean Privat <jean@pryen.org>
lib/string_search: more documentation and nitunit tests

Fixes #186
Fixes #218
Signed-off-by: Jean Privat <jean@pryen.org>
lib/environ: more documentation and nitunit tests

Fixes #209
Signed-off-by: Jean Privat <jean@pryen.org>
Merge branch 'doc_stdlib_some_more'