New grammar will allow statements ending without semicolon as disccused in Issue #38

Flow grammer is modified to allow each line ending without semicolon to improve readablity. The old declarations also work. One test is also included in flow.spec.js to test the changes. 

After merging this change, declaration of a graph as defined below becomes possible : 

```
graph TD
        sq[Square shape] --> ci((Circle shape))
        od>Odd shape] ---|Two line<br>edge comment| ro
        od2>Really long text in an Odd shape] --> od3>Really long text with linebreak<br>in an Odd shape]
        di{Diamond is <br/> broken} --> ro(Rounded<br>square<br>shape)
        di --> ro2(Rounded square shape)
        %% Comments after double percent signs
        e((Inner / circle)) --> f(,.?!+-*ز)
        cyr[Cyrillic] --> cyr2((Circle shape Начало))
        style e red
```

After this the Issue #38 can be closed.