org.texi: Reword Babel chapter

* doc/org.texi (Template elements):
(Tables in @LaTeX{} export):
(Working with source code):
(Structure of code blocks):
(Editing source code):
(Exporting code blocks):
(Extracting source code):
(Evaluating code blocks):
(Library of Babel):
(Languages):
(Header arguments):
(Using header arguments):
(System-wide header arguments):
(Language-specific header arguments):
(Header arguments in Org mode properties):
(Language-specific header arguments in Org mode properties):
(Code block specific header arguments):
(Header arguments in function calls):
(Specific header arguments):
(var):
(results):
(file-desc):
(file):
(output-dir):
(dir):
(exports):
(comments):
(padline):
(no-expand):
(session):
(noweb):
(noweb-ref):
(noweb-sep):
(cache):
(sep):
(hlines):
(colnames):
(rownames):
(shebang):
(tangle-mode):
(eval):
(wrap):
(post):
(prologue):
(Results of evaluation):
(Noweb reference syntax):
(Key bindings and useful functions):
(Batch execution): Improve wording.