Bump to 1.4.0
Skip fastestmirror detection of only one mirror is present
downloader: Call LR_PROGRESSCB with zeroized values, when total_to_download value is changed.

Only during metadata downloading.
Behaviour during package downloading is still the same.
downloader: check return value from progresscb
Enable checksum caching for already existing local packages
download_packages: Add lr_check_packages()
Close the correct file when using a metalink.xml file

When using librepo, PackageKit crashes after after issuing a few hundred
transactions with 'Too many open files' -- Sure enough, looking at the output
of lsof before it crashes, I have hundreds of open files to various metalink.xml
files.

Fix the typo so that the metalink file descriptor actually gets closed.
Add LRR_YUM_TIMESTAMP (GitHub issue #25)
Extend C example
tests: Fix python3 syntax error in python test
Bump to 1.5.0
Sanitize progresscb.