ob: Support for exporting inline source code

ob: Support for exporting inline source code

* lisp/ob-exp.el (org-babel-exp-inline-code-template): New
customizable variable to export inline source code (similar to
`org-babel-exp-code-template').
(org-babel-exp-code): New `type' argument to differentiate between
inline and standard code blocks.

* lisp/ob-core.el (org-babel-inline-src-block-regexp): Allow empty set
of switches and header arguments as in "src_sh[]{echo foo;}".  Also
permit spaces before them.

* testint/lisp/test-org-element.el
(test-org-element/inline-src-block-parser): Test extended syntax for
inline source code.

* testing/lisp/test-ob-exp.el (ob-exp/exports-inline-code): New
function for testing inline source code handling.  Also add three new
failing tests exhibiting unexpected results with ":results code"
switches.

* testing/lisp/test-ob.el
(test-org-babel/org-babel-get-inline-src-block-matches): Test for
inline source blocks with empty header arguments.

* testing/examples/babel.org: New sections for testing (i) exported
inline source code (used by `ob-exp/exports-inline-code'); (ii)
parsing inline source blocks with empty header arguments (used by
`test-org-babel/org-babel-get-inline-src-block-matches').

Until now pieces of inline source code were handled as standard code
blocks during export.  These changes enable them to be exported.