Enable the equal sign in the file mask

In the lfs project (see  https://github.com/Canop/lfs) there are a number of image files containing an equal sign resulting in the warning like:
```
.../README.md:28: warning: image file website/docs/img/c is not found in IMAGE_PATH: assuming external image.
```
whilst the line in the code reads:
```
![screenshot](website/docs/img/c=label+default+dev.png)
```
and the mentioned image does exist

(Found through Fossies)

Author: albert-github

src/commentscan.l

@@ -495,8 +495,8 @@ ATTR      ({B}+[^>\n]*)?
 DOCNL     "\n"|"\\ilinebr"
 LC        "\\"{B}*"\n"
 NW          [^a-z_A-Z0-9]
-FILESCHAR [a-z_A-Z0-9\x80-\xFF\\:\\\/\-\+@&#]
-FILEECHAR [a-z_A-Z0-9\x80-\xFF\-\+@&#]
+FILESCHAR [a-z_A-Z0-9\x80-\xFF\\:\\\/\-\+=@&#]
+FILEECHAR [a-z_A-Z0-9\x80-\xFF\-\+=@&#]
 FILE      ({FILESCHAR}*{FILEECHAR}+("."{FILESCHAR}*{FILEECHAR}+)*)|("\""[^\n\"]*"\"")
 ID        [$a-z_A-Z\x80-\xFF][$a-z_A-Z0-9\x80-\xFF]*
 LABELID   [a-z_A-Z\x80-\xFF][a-z_A-Z0-9\x80-\xFF\-]*

src/doctokenizer.l

@@ -279,8 +279,8 @@ ATTRIB    {ATTRNAME}{WS}*("="{WS}*(("\""[^\"]*"\"")|("'"[^\']*"'")|[^ \t\r\n'"><
 URLCHAR   [a-z_A-Z0-9\!\~\,\:\;\'\$\?\@\&\%\#\.\-\+\/\=\x80-\xFF]
 URLMASK   ({URLCHAR}+([({]{URLCHAR}*[)}])?)+
 URLPROTOCOL ("http:"|"https:"|"ftp:"|"ftps:"|"sftp:"|"file:"|"news:"|"irc:"|"ircs:")
-FILEICHAR [a-z_A-Z0-9\\:\\\/\-\+&#@]
-FILEECHAR [a-z_A-Z0-9\-\+&#@]
+FILEICHAR [a-z_A-Z0-9\\:\\\/\-\+=&#@]
+FILEECHAR [a-z_A-Z0-9\-\+=&#@]
 FILECHARS {FILEICHAR}*{FILEECHAR}+
 HFILEMASK {FILEICHAR}*("."{FILEICHAR}+)+{FILECHARS}*
 VFILEMASK {FILECHARS}("."{FILECHARS})*