Readme: Fix clang badge URL.
Merge pull request #1095 from fwalch/fix-clang-badge-url

Readme: Fix clang badge URL.
Document globpath().
Simplify globpath().

Factor out common subexpression: `WILD_SILENT|expand_options`.

Prefer `continue` to excessive indentation in loop.
Simplify ExpandRTDir().

 * Return `bool`.
 * Use concat_str and `concat_fnames` over `xmalloc()`/`snprintf()`.
 * Use `fnamencmp()` over `STRNICMP()`.
 * Replace variable `e` with `dot`.