docs: correctly refer to the readthedocs page for current docs (#2104)

I found some places that still referred to the old PDF document in the
repo, but we haven't used that for a while and no longer build it.

Also remove some chunks of the Makefile that used to be responsible
for building the LaTeX docs, since those don't even exist in the repo
any more.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

README.md

@@ -479,21 +479,8 @@ how to build and install OSL.
 Documentation
 -------------
 
-The OSL language specification can be found at
-[src/doc/osl-languagespec.pdf](src/doc/osl-languagespec.pdf) (in a source
-distribution) or in the share/doc/OSL/osl-languagespec.pdf file of an
-installed binary distribution.
-
-[OSL Documentation on ReadTheDocs](https://docs.openshadinglanguage.org)
-This will be the future documentation. It's probably as complete as the PDF,
-but it needs some proofreading, so the PDF is still considered the
-authoritative source for now. But some time soon, the old PDF specification
-will be deprecated in favor of
-this online documentation.
-<!-- is the best place to start if you are interested in how to use OSL,
-its APIs. -->
-There is also a [PDF
-version](https://readthedocs.org/projects/open-shading-language/downloads/pdf/latest/).
+The OSL language specification can be found at [OSL Documentation on ReadTheDocs](https://docs.openshadinglanguage.org)
+There is also a [PDF version](https://readthedocs.org/projects/open-shading-language/downloads/pdf/stable/).
 
 For those interested in learning to program OSL shaders there is the
 [Siggraph 2024 Course](https://dl.acm.org/doi/proceedings/10.1145/3664475), 
@@ -544,16 +531,14 @@ Contacts, Links, and References
 
 [OSL GitHub page](https://github.com/AcademySoftwareFoundation/OpenShadingLanguage)
 
-[Read or subscribe to the OSL development mail list](https://lists.aswf.io/g/osl-dev)
+[OSL Documentation on ReadTheDocs](https://docs.openshadinglanguage.org)
 
-[Most recent PDF of the OSL language specification](https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/blob/main/src/doc/osl-languagespec.pdf
-)
+[Read or subscribe to the OSL development mail list](https://lists.aswf.io/g/osl-dev)
 
 [OSL home page](http://openshadinglanguage.org)
 
 
 
-
 Credits
 -------
 

src/doc/Makefile

@@ -2,31 +2,12 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # https://github.com/AcademySoftwareFoundation/OpenShadingLanguage
 
-PDFLATEX_FLAGS = -interaction=errorstopmode   ###  "--shell-escape"
 
+# by default, make the sphinx documentation
+all: doxygen sphinx
 
-# by default, just make the document
-all: languagespec.pdf
 
-
-# document making rule: use pdflatex
-languagespec.pdf: *.tex Figures/*.pdf Figures/*png
-	pdflatex ${PDFLATEX_FLAGS} languagespec.tex
-
-
-
-# special command 'make index' to regenerate the index
-index: languagespec_index
-
-languagespec_index:
-	pdflatex ${PDFLATEX_FLAGS} languagespec.tex
-	makeindex languagespec
-	pdflatex ${PDFLATEX_FLAGS} languagespec.tex languagespec.aux macros.aux
-	pdflatex ${PDFLATEX_FLAGS} languagespec.tex languagespec.aux macros.aux languagespec.toc
-
-clean:
-	rm -f languagespec.aux languagespec.idx languagespec.ilg languagespec.ind languagespec.log
-	rm -f languagespec.out languagespec.pdf languagespec.toc macros.aux
+clean: doxygenclean
 
 .PHONY: clean