Allow header or alignment to have extra spaces at the end or not balanced

[tomyeh]

1. Extra spaces at the end

If there is extra spaces at the end of the header row or the alignment row, the table won't be generated.

Unfortunately, it is hard to detect for end users. Thus, it is better to simply remove them if possible.

| head | cells |  
|------|-------|
| body | cells |

2. Not balanced

| head | cells |
|------|
| body | cells |

3. No header

| --- |
| bar |