dvisvgm 2.1

Changes

• Added option --tmpdir to explicitly set folder for temporary files.
• Temporary files are no longer created in the current working directory by default but in the system's temp folder (fixes #63).
• Added warning/error messages if temporary files could not be written.
• Fixed collision of Unicode points in AGL table (fixes #64).
• Retain letter case of filenames even if it's not significant (Windows only).
• Various code refactorings and code cleanup.