Refined behaviors in existing commands and options

Nvi2 now generates headers under the build directory to further
improve the out-of-source build. Please check #143 to understand
the impact on porting.

Changes:

• New option showfilename (#129)
• Show percentage in addition to line counts in ruler (#131)
• Fixed a segfault in expandtab (#154)
• Improve POSIX-compliance when handling ex insert empty lines (#156, #157)
• Counted-p pastes without interleaving copied content (#150)
• Code in analyzer-friendly style (#122, #124)
• Portability fixes (#125, #155)

Full Changelog: v2.2.1...v2.2.2

macOS port, Linux port, and new option

Fifteen contributors, can you believe? Thank all of you.

Changes:

• macOS port (#89, #91, #99)
• Linux port (#82, #83)
• Display control chars in altnotation (#117)
• Intuitively jump between troff paragraphs (#119)
• UI fixes (#81, #107, #115)
• Stability fixes (#39, #96, #97, #98, #106, #111)
• Improving the documentation (#85, #93, #114)

Expandtab option and Turkish translation

Nvi2 has moved to out-of-source build. Please read #79 to familiarize
yourself with the new workflow.

Changes:

• Vim-style expandtab option (#75, #76, #80)
• Provides Turkish translation (#68)
• Backspace now deletes \ rather than being escaped (#25)
• T during motion commands is now VI-compatible (#35)
• Encoding related fixes, such as UTF-8 detection (#61, #42, #65)
• Fixed a number of memory management issues (#56)

Improve stability and cleanup code

• Files containing encoding errors can be correctly saved (#12)
• Terminal resizing is much improved (#32)
• Fallback terminal type is changed to ansi (023d7e6)
• -R (:se readonly) option affects split screens (f70a26c)
• mdoc(7) manpages came from OpenBSD (#9)