docs: fix typos in manual, and a couple in code comments.

docs: fix typos in manual, and a couple in code comments.

* doc/ref/api-binding.texi, doc/ref/api-compound.texi,
doc/ref/api-control.texi, doc/ref/api-debug.texi,
doc/ref/api-io.texi, doc/ref/api-macros.texi,
doc/ref/api-procedures.texi, doc/ref/api-scheduling.texi,
doc/ref/api-undocumented.texi, doc/ref/api-utility.texi,
doc/ref/compiler.texi, doc/ref/goops.texi,
doc/ref/libguile-concepts.texi, doc/ref/misc-modules.texi,
doc/ref/posix.texi, doc/ref/r6rs.texi, doc/ref/slib.texi,
doc/ref/srfi-modules.texi, doc/ref/sxml-match.texi,
doc/ref/tools.texi, doc/ref/vm.texi, doc/ref/web.texi,
doc/sources/env.texi, doc/sources/jimb-org.texi,
doc/sources/scheme-concepts.texi, doc/sources/unix.texi,
module/ice-9/optargs.scm: Fix typos.
* doc/r4rs/r5rs.texi: Likewise.  Do not capitalize code symbols
even at the start of a sentence.
* doc/ref/api-data.texi: Likewise.  Also, remove executable bit.