Note author of %r macros idea

Forgot to do this in appropriate branch.
Fix memory error on expanding tabulation symbols
Save dot files filter state of views in vifminfo

Closes #5.
Note dot filter saving in documentation
Cache line[0] in a variable in read_info_file()
Cache line[0] in a variable in update_info_file()
Cache line + 1 in a variable in read_info_file()
Cache line[0] in a variable in update_info_file()

Also added const qualifier to type of the only parameter of
get_viewer_for_file() function.
Use macros for chars specific to vifminfo file
Use line_val in read_info_file() more intensively
Add and use register_exists() function
Unset GIT_DIR envvar in Makefile

This fixes generating of compile_info.c file when it's called from
pre-commit hook.
Fix terminal issues after running Vim from make
Merge branch 'save-dotfiles-filter-in-vifminfo'