Remove modeline before creating file parser

This makes NEWS and other files look good.  This also deletes the
modeline from ruby files, but this should be harmless as those parsers
don't currently care about the modeline.

Fixes #178
Output proper HTML markup for markdown input

RDoc formatters process inline markup on a paragraph-by-paragraph basis.
If this is not done then embedded markup in that paragraph will not be
output correctly.

Now the paragraph's contents are joined into a single line before
processing which allows the formatter to generate the correct output.

Fixes #204
Use ruby 2.0.0, not ruby-head, for travis
Restrict fix for #204 to HTML only

Replacing newlines with spaces in paragraphs for other output leads to
missing line breaks and incorrect output.
Added test for #180

When loading a class or module from the RDoc store then reparsing its
source file the old comment is replaced with the new comment.

This also means that if a module or class is mentioned multiple times in
the same file RDoc will only use the last comment.

These two behaviors of the comment conflict, so I must delay fixing this
issue until the future while I think about it.
Remove nodoc items when storing a class or module

Since the document_self and ignored properties are not included in the
store, items with these flags should also be removed from the output.

This prevents the items from incorrectly showing up in the RDoc servlet
or through ri.

Fixes #177
Create ToHtmlSnippet correctly in Text#snippet

While ToHtmlSnippet was updated to pass an Options instance in,
Text#snippet was not.  This has been corrected by adding
RDoc::CodeObject#options which uses the store's options or creates a
default RDoc::Options instance.

This bug was missed in part due to commented-out tests for Text#snippet.
Separate C call-seq for "copied" methods

If the same C function is used to implement two methods typically the
call-seq in the comment describes both methods together.

This leads to confusing duplication in generated HTML as identical
content is show twice.

Now when such a method is encountered the call-seq is de-duplicated to
avoid this confusion.
Work around ruby 1.8.7 differences
Update version, release pending
Fix unused variable warnings
Prevent RI Driver test from loading ~/.rdoc

On ruby 1.8 this will fail as the ri data contains references to
Encoding which is not present.