Add simple Doxygen filter for Julia

Also modifies Doxyfile to accept Julia source files, telling doxygen to
parse Julia files with its C parser. Now of course Julia is NOT C at
all, but doxygen allows you to fool it by running input filters on
source files.

The Julia-to-pseudo-C filter is the most brain-dead thing you can
imagine. All the heavy lifting is done by JuliaParser.jl; the filter
simply looks for function declarations, rewrites the signatures into
pseudo-C notation, and then spits out the body of the function parsed by
JuliaParser wrapped with a pair of braces.

The pseudo-C function signature is quite incomplete:
- varargs drop the names of the variable (e.g. myarrays... -> ....),
- kwargs are ignored

Nonetheless it's quite amazing how much functionality you can get from
such a terrible hack!

contrib/Doxyfile

@@ -280,7 +280,7 @@ OPTIMIZE_OUTPUT_VHDL = NO
 # Note that for custom extensions you also need to set FILE_PATTERNS otherwise
 # the files are not read by doxygen.
 
-EXTENSION_MAPPING =
+EXTENSION_MAPPING = jl=C
 
 # If the MARKDOWN_SUPPORT tag is enabled then doxygen pre-processes all comments
 # according to the Markdown format, which allows for more readable
@@ -772,7 +772,7 @@ INPUT_ENCODING = UTF-8
 # *.md, *.mm, *.dox, *.py, *.f90, *.f, *.for, *.tcl, *.vhd, *.vhdl, *.ucf,
 # *.qsf, *.as and *.js.
 
-FILE_PATTERNS = *.c *.cpp *.h
+FILE_PATTERNS = *.c *.cpp *.h *.jl
 
 # The RECURSIVE tag can be used to specify whether or not subdirectories should
 # be searched for input files as well.
@@ -866,14 +866,14 @@ INPUT_FILTER =
 # filters are used. If the FILTER_PATTERNS tag is empty or if none of the
 # patterns match the file name, INPUT_FILTER is applied.
 
-FILTER_PATTERNS =
+FILTER_PATTERNS = *.jl=/Users/jiahao/sandbox/jldoxy/doxyfilter.jl
 
 # If the FILTER_SOURCE_FILES tag is set to YES, the input filter (if set using
 # INPUT_FILTER ) will also be used to filter the input files that are used for
 # producing the source files to browse (i.e. when SOURCE_BROWSER is set to YES).
 # The default value is: NO.
 
-FILTER_SOURCE_FILES = NO
+FILTER_SOURCE_FILES = YES
 
 # The FILTER_SOURCE_PATTERNS tag can be used to specify source filters per file
 # pattern. A pattern will override the setting for FILTER_PATTERN (if any) and

contrib/doxyfilter.jl

@@ -0,0 +1 @@
+/Users/jiahao/sandbox/jldoxy/doxyfilter.jl