Parsetools fix unicode leex

    %% -*- coding: utf-8 -*-
    Definitions.
    RTLarrow    = (←)
    Rules.
    {RTLarrow}  : {token,{'<-',TokenLine}}.
    Erlang code.

This code would either not work as intended (which is build a lexer capable of recognizing a unicode arrow)
or crash at compile time.

An error was thrown when compiling this code (put inside lexer.xrl):

    unexpected error compiling src/lexer.xrl
    {'EXIT',{badarg,[{re,run,
                         [[83,121,109,98,111,108,32,32,32,32,32,32,61,32,40,91,36,
                           163,8364,93,124,91,60,62,61,93,41,10],
                          "^[ \t]*([A-Z_][A-Za-z0-9_]*)[ \t]*=[ \t]*([^ \t\r\n]*)[ \t\r\n]*$",
                          [{capture,all_but_first,list}]],
                         []},
                     {leex,parse_defs,4,[{file,"leex.erl"},{line,439}]},
                     {leex,parse_file,1,[{file,"leex.erl"},{line,407}]},
                     {leex,file,2,[{file,"leex.erl"},{line,112}]},
                     {rebar_erlc_compiler,compile_xrl_yrl,5,
                                          [{file,"src/rebar_erlc_compiler.erl"},
                                           {line,429}]},
                     {rebar_base_compiler,compile,3,
                                          [{file,"src/rebar_base_compiler.erl"},
                                           {line,121}]},
                     {rebar_base_compiler,compile_worker,3,
                                          [{file,"src/rebar_base_compiler.erl"},
                                           {line,194}]}]}}

This commit fixes said error and enables Erlang's Leex to build lexers for Unicode languages.