Problem:    Cannot build with Ruby.
Solution:   Fix misplaced brace.

Problem:    W_WIDTH() is always the same.
Solution:   Expand the macro.

Problem:    FEAT_WINDOWS adds a lot of #ifdefs while it is nearly always
            enabled and only adds 7% to the binary size of the tiny build.
Solution:   Graduate FEAT_WINDOWS.

Problem:    Buffer overflow in Ruby.
Solution:   Allocate one more byte. (Dominique Pelle)

Problem:    May get ml_get error when :rubydo deletes lines or switches to
            another buffer. (Nikolai Pavlov, issue #1421)
Solution:   Check the buffer and line every time.

Problem:    Some systems do not have ruby_sysinit(), causing the build to
            fail.
Solution:   Clean up how ruby_sysinit() and NtInitialize() are used. (Taro
            Muraoka)

Problem:    Building with a new Ruby version fails.
Solution:   Use ruby_sysinit() instead of NtInitialize(). (Tomas Volf,
            closes #1382)

Problem:    Ruby 2.4 no longer supports rb_cFixnum.
Solution:   move rb_cFixnum into an #ifdef. (Kazuki Sakamoto, closes #1365)

Problem:    Modelines in source code are inconsistant.
Solution:   Use the same line in most files.  Add 'noet'.  (Naruhiko Nishino)

Problem:    Looping over windows, buffers and tab pages is inconsistant.
Solution:   Use FOR_ALL_ macros everywhere. (Yegappan Lakshmanan)