WriteTeX v0.4 is released

These two days, several improvements have been made to WriteTeX. The main flaws in the code are fixed. The version is too small to reflect the progress of the project. Therefore, I decided to release the extension at a version number of v0.4. Main changes of this release are

• Preamble can be type directly into the preamble box.
• Error handling for latex compilation errors.
As is noted in the commit message, maybe pdfcrop will be added to the dependency list. If the scale problem is solved, the extension will be very close to finally release.