Process line break: force-multiline & tests

[tinyAdapter]

This PR enhances #558 with new features and tests.

In short, the preprocessor now does not consider any lines with -concat as a new line. This prevents the ambiguity of statements like

aaa 
|bbb -concat

being preprocessed as one line

aaa|bbb -concat
;_WEBGAL_LINE_BREAK_|bbb -concat

but breaks the original grammar of "show aaa at the first line, then show bbb at the second line when user clicks".

---

Now, the preprocessor will not handle this, only outputting

aaa 
|bbb -concat

---

The user can forcely enable multiline support in such case by adding \ to the end of the first line, i.e.,

aaa\
|bbb -concat

which will be preprocessed as

aaa|bbb -concat
;_WEBGAL_LINE_BREAK_|bbb -concat