VOICP — Textual syntax adjustments

Some adjustments to the textual syntax are needed.
In particyular:
Allow decision with empty decision expression decision ()

Operator != is missing in BNF (found '<>' instead)

(1) In Section 10.2, after "This section gives formally the grammar.", adds the following paragraph:

Lexical elements:

The list of reserved words is:
'service', 'voiceservice', 'entities', 'package', 'class', 'operation', 'message', 'messagepart', 'event', 'externalevent', 'systemevent', 'static', 'global', 'shared', 'property', 'var', 'extends','maindialog', 'dialog', 'within', 'in','inout','out', 'behavior', 'play', 'playall', 'call', 'divert', 'return', 'stop', 'decision', 'case', 'junction', 'jump', 'restart', 'wait', 'when', 'do', 'accept', 'if', 'then', 'else', 'endif', 'null', 'true', 'false', 'unlimited', 'not', 'and','or','xor'','informal','new','Set','Bag','Sequence','OrderedSet'.

In the BNF these keywords are denoted by the corresponding word in capital letters. For instance DIALOG denotes the occurrence of the dialog keyword.

The following variable tokens are defined:

ID: an alphanumeric identifier
ICONST: integer value
FCONST: float value
SCONST: double quoted string
CCONST: single quoted string

The following character tokens are defined:
'PLUS' -> '+'
'MINUS' > ''
'TIMES' -> '*'
'DIVIDE' -> '/'
'MOD' -> '%'
'EQ' -> '=='
'LT' -> '<'
'LE' -> '<='
'LT' -> '<'
'GE' -> '>='
'GT' -> '>'
'NE' -> '<>'
'NEX' -> '!='
'EQUALS' -> '='
'PLUSEQUAL' -> '+='
'MINUSEQUAL' > '='
'ARROW' > '>'
'PERIOD' -> '.'
'LPAREN' -> '('
'RPAREN' -> ')'
'LBRACKET' -> '['
'RBRACKET' -> ']'
'LBRACE' -> '

'
'COMMA' -> ','
'SEMI' -> ';'
'COLON' -> ':'
'DCOLON' -> '::'

(2) Replace the BNF rule:
decision_head LBRACE decision_body RBRACE
by
decision_head LBRACE decision_body? RBRACE