Allow specifying color= in shellcheckrc (closes #2350)

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## Git (0.8.0)
 ### Added
+- `color=` directive can be added to .shellceckrc
 - `disable=all` now conveniently disables all warnings
 - `external-sources=true` directive can be added to .shellcheckrc to make
   shellcheck behave as if `-x` was specified.

shellcheck.1.md

@@ -41,7 +41,10 @@ not warn at all, as `ksh` supports decimals in arithmetic contexts.
 
 :   For TTY output, enable colors *always*, *never* or *auto*. The default
     is *auto*. **--color** without an argument is equivalent to
-    **--color=always**.
+    **--color=auto**.
+
+    This option may also be enabled using `color=` in
+    `.shellcheckrc`. This flag takes precedence.
 
 **-i**\ *CODE1*[,*CODE2*...],\ **--include=***CODE1*[,*CODE2*...]
 
@@ -232,6 +235,10 @@ Here a shell brace group is used to suppress a warning on multiple lines:
 
 Valid keys are:
 
+**color**
+:   Set to `auto`, `never` or `always` in `.shellcheckrc` to automatically
+    detect, never or always use color output with the `tty` output format.
+
 **disable**
 :   Disables a comma separated list of error codes for the following command.
     The command can be a simple command like `echo foo`, or a compound command
@@ -277,6 +284,9 @@ it will read `key=value` pairs from it and treat them as file-wide directives.
 
 Here is an example `.shellcheckrc`:
 
+    # Always force color output on the tty output
+    color=always
+
     # Look for 'source'd files relative to the checked script,
     # and also look for absolute paths in /mnt/chroot
     source-path=SCRIPTDIR

src/ShellCheck/Parser.hs

@@ -1005,6 +1005,14 @@ readAnnotationWithoutPrefix sandboxed = do
         key <- many1 (letter <|> char '-')
         char '=' <|> fail "Expected '=' after directive key"
         annotations <- case key of
+            "color" -> do
+             color <- many1 $ noneOf " \n"
+             option <- parseColorOption color
+             return options {
+                 formatterOptions = (formatterOptions options) {
+                     foColorOption = option
+                 }
+             }
             "disable" -> readElement `sepBy` char ','
               where
                 readElement = readRange <|> readAll