Don't require quoting for non-alphanum characters

This commit removes the one remaining (known) difference with the sysdig
c++ parser: relational expression right-hand sides now _only_ need to be
quoted if they contain a paren or a space.

So you can now do things like "fd.name contains (.log and event.dir = <"
without needing to quote "*.log" or "<".

lua/parser-smoke.sh

@@ -50,17 +50,19 @@ good "a.b icontains 'bla'"
 good "a.g in ()"
 good "a.g in (1, 'a', b)"
 good "a.g in ( 1 ,, , b)"
+good "evt.dir=> and fd.name=*.log"
+good "evt.dir=> and fd.name=/var/log/httpd.log"
+good "a.g in (1, 'a', b.c)"
+good "a.b = a.a"
 
-bad "a.g in (1, 'a', b.c)"
-bad "a.b = a.a"
 bad "(a.b = 1"
-
 # Macros
 
 good "a: a.b exists"
 good "a: b and c"
 good "a: b"
 good "a : b"
+good "a : evt.dir=>"
 good "inbound: (syscall.type=listen and evt.dir='>') or (syscall.type=accept and evt.dir='<')"
 bad "a:"
 

lua/sysdig-parser.lua

@@ -7,14 +7,9 @@
 
    inbound: (syscall.type=listen and evt.dir='>') or (syscall.type=accept and evt.dir='<')
 
-   (*) There are a few minor differences with the syntax implemented in libsinsp:
+   (*) There currently one known difference with the syntax implemented in libsinsp:
 
-   - (Feature!) In libsinsp, field names cannot start with 'a', 'o', or 'n'. With this parser they can
+   - In libsinsp, field names cannot start with 'a', 'o', or 'n'. With this parser they can
-
-   - (Bug!) In libsinsp, operator right-hand sides only need to be quoted if they contain spaces or parens. With this parser, they need to be quoted if they contain any non-alphanumeric character. For example:
-
-   (libsinsp)    fd.name = mylog or fd.name contains .log and event.dir = <
-   (this parser) fd.name = mylog or fd.name contains '.log' and event.dir = '<'
 
 ]]--
 
@@ -197,7 +192,7 @@ local G = {
   MacroDef = (C(V"Macro") * V"Skip" * V"Colon" * (V"Filter"));
 
   -- Terminals
-  Value = terminal "Number" + terminal "String" + terminal "Identifier";
+  Value = terminal "Number" + terminal "String" + terminal "BareString";
 
   InList = symb("(") * list(V"Value", symb(",")) * symb(")");
 
@@ -220,6 +215,8 @@ local G = {
   Number = C(V"Hex" + V"Float" + V"Int") /
            function (n) return tonumber(n) end;
   String = (P'"' * C(((P'\\' * P(1)) + (P(1) - P'"'))^0) * P'"' +  P"'" * C(((P"\\" * P(1)) + (P(1) - P"'"))^0) * P"'")  / function (s) return fix_str(s) end;
+  BareString = C(((P(1) - S' (),'))^1);
+
   OrOp = kw("or") / "or";
   AndOp = kw("and") / "and";
   Colon = kw(":");