Relative Links
Merge Charley Peng's changes for relative links

Merge branch 'local' of https://github.com/chid/mathb.
Add system setup details for static preview

MathB uses tools like pandoc and convert to display static
preview of the rendered code for clients where JavaScript is
disabled. These tools need to be installed for static preview to
work correctly. Add the details about the packages to be
installed in the README file.
Display preview button when JavaScript is disabled

When JavaScript is disabled, the user cannot see a live preview
of the rendered code. A preview button can help the user to see
a static preview (rendered with an image) before he or she saves
the post. The preview button should be displayed if and only if
JavaScript is disabled.
HTML-like paragraphs in static preview

HTML paragraphs do not have their text indented. There is
vertical blank space between two paragraphs in HTML. The static
preview though behaves like the default paragraphs rendered with
LaTeX.  They do not have any vertical space between them and the
first line of each paragraph is indented.

This issue occurs even though \setlength commands have been used
for \parindent and \parskip in the LaTeX template being used
with the pandoc command. The \setlength commands occur before
\begin{document} command, and this seems to be causing an issue
with the standalone document class. When the \setlength commands
are moved after the \begin{document} command, this issue is
resolved.
Display error message in static preview on error

If an error occurs while converting the input code to PNG image
for static preview, then create a PNG image to display the error
that occurred.
Add 'Features' section to README

The 'Features' section in README is meant to enumerate all the
significant features of this application.
Fix static preview error due to missing PDF

While converting the input code to PNG image for static preview,
MathB\Preview is deleting the intermediate PDF too early, after
running the pandoc command to convert the input code to PDF.
Therefore, when the convert command runs to convert the PDF to
PNG, it fails. Fix this by moving the code to delete the PDF
after the convert command converts the PDF to PNG.
URL to mathb.in in 'Features' section of README

Add an introductory paragraph and an URL to http://mathb.in in
the 'Features' section in the README.md file.
Merge branch 'master' of https://github.com/susam/mathb