Reassign variable names : still considering (but not replacing) text in strings

[Siorki]

Issue found while working on my entry in js1k 2017.

The module log lists $ as variable, although I only use it in template strings. This can still be observed with the final code for the demo.

A new name is assigned for it, however it does not get replaced inside the string (see #57) so the output is correct.

However, the new name is squandered - it could have been assigned to another (real) variable instead. If there are not enough names left, this would lead to a character being unnecessarily allocated from outside the name pool, effectively removing a possible token.

[Siorki]

Example code showing the issue, used in the non-regression test for #82

p=c.getImageData(0,0,512,512);d=p.data;for(j=0;j<512;++j){c.fillStyle=`#${`200`,`300`,`fff`,`000`][j&3]}`;d[j*4]=0;d[j*4+1]=255;d[j*4+2]=j>>1;d[j*4+3]=0;c.beginPath();c.moveTo(0,j);c.lineTo(511,j);c.stroke();}

$ gets renamed to D, even though there is no D showing in the preprocessed code.

[Siorki]

Added an identification of template literals, stored in PackerData.

Variable identification and replacement are only performed outside of strings and inside template literals.

01b66ea