Add flags option to request JSON

Adds a `flags` parameter to the request JSON, appearing under the `compile.options` key (alongside such stalwarts as `compiler`, `timeout`, etc.).

This is primarily to support `-file-line-error` as an option, but could have other uses as well.

`flags` should be an array of strings, or absent. If supplied, the listed arguments are added to the base latexmk command.

test/unit/coffee/LatexRunnerTests.coffee

@@ -59,3 +59,21 @@ describe "LatexRunner", ->
 				mainFile = command.slice(-1)[0]
 				mainFile.should.equal "$COMPILE_DIR/main-file.tex"
 
+		describe "with a flags option", ->
+			beforeEach ->
+				@LatexRunner.runLatex @project_id,
+					directory: @directory
+					mainFile:  @mainFile
+					compiler:  @compiler
+					image:     @image
+					timeout:   @timeout = 42000
+					flags:     ["-file-line-error", "-halt-on-error"]
+					@callback
+
+			it "should include the flags in the command", ->
+				command = @CommandRunner.run.args[0][1]
+				flags = command.filter (arg) ->
+					(arg == "-file-line-error") || (arg == "-halt-on-error")
+				flags.length.should.equal 2
+				flags[0].should.equal "-file-line-error"
+				flags[1].should.equal "-halt-on-error"