This commit fixes a bug in parsing indented literal blocks. For example:
test(8)
```
This is a block
```
Prior to this commit, this would fail, but with an unexpected error
message: "Error at 4:3: Cannot deindent in literal block". The
indentation was being parsed at every character, so the parser saw the
`T`, then parsed indentation again. The indentation was 0 (since there
were no tab characters between the `T` and the `h`), but the block
started with an indentation level of 1. 0 < 1, so this would be
considered a dedent, which is not allowed.
This commit introduces a new local variable, `check_indent`, which
controls whether the parser tries to parse indentation or not; now
indentation is only parsed when the last character was a newline. From
my testing this seems to fix the issue - indented literal blocks are now
allowed.