Escaping expressions (ESC_VAR) does not work for raw vars or any custom delimiter

[JonMcPherson]

The ESC_VAR lexer function which supports escaped handlebars expressions using a backslash, only works for normal expressions that are defined using 2 curly brackets like \{{var}}, but it does not work for raw expressions \{{{rawVar}}}, or any custom delimiters \[[var]], giving a false syntax error:

com.github.jknack.handlebars.HandlebarsException: inline@f73de56:1:1: found: '\'
\{{{foo}}}
 ^

If you add these test cases to the Issue #294 test suite (original support for escaped vars), then you should see this error. This is a bug since it should be supported according the Handlebars spec.

@Test
public void escapeRawVars() throws IOException {
  shouldCompileTo("\\{{{foo}}}", $, "{{{foo}}}");
}

@Test
public void escapeRawVarsWithText() throws IOException {
  shouldCompileTo("before \\{{{foo}}} after", $, "before {{{foo}}} after");
}

I've added support in this PR #1085