Fix invalid read in find_bytes().

Validate arguments. Move the conditional to the start of the loop
to avoid an invalid read if len < slen.

Closes issue #21.
Disable tests which are hanging with valgrind.

find_bytes() rejecting invalid arguments hangs some valgrind tests.
They appear to be segfaulting inside std:vector faster than valgrind
can process the signals.

This should be re-enabled when the problem is resolved.
Fixes #133 - Correct assertions

- ASSERT_TRUE( isHorizontal() )
- ASSERT_FALSE( isVerticalRightToLeft() ) and ASSERT_FALSE(
  isVerticalLeftToRight() ) in order to check multiple code paths
- ASSERT_EQ( 1, errorCount() ) for safety
- Use convenience assertEquals function to save space
- Comments wrapped to 80 columns but otherwise unchanged
Fixes #134 - Corrected assertion, safety checks, wrapped lines

- Assert that isHorizontal==true, isVerticalLeftToRight and
  isVerticalRightToLeft are both false
- Assert that we have 1 error to prevent segfault
- Use convenience error checker to shrink line count
- Assert error code is BAD_VALUE rather than UNEXPECTED_WHITESPACE
- Wrap comments to 80 columns, and correct them to match test
Merge pull request #131 from rillian/issue-39

Fix find_bytes and disable hanging unit tests.
Merge pull request #134 from caitp/issue-134

CueSettingVertical.UppercaseValue -- ASSERT_EQ( 50, isHorizontal() )
Fix segfaults in ExtraNewLinesAfterCue.

I've fixed the segfaul in FileStructure.ExtraNewLinesAfterCue.
Problem was that it was trying to parse a cue when it got to the
end of the buffer and there was just new lines after it. I've set it
up to now consume all white space after a cue or cue text has been
parsed. It's seemed to fix a lot of the other tests too.
Add param checks to skipwhite function.

I've added param checks to the new webvtt_skipwhite function. I've
also moved the respective webvtt_skipwhite functions to their
respective files so that the names do not conflict with one another.