Initial easybook chapter (#1129)

* some mdbook #785

* more chapter 1

CMakeLists.txt

@@ -1,3 +1,4 @@
+# 3.14.0 introduced NAME_WLE
 cmake_minimum_required(VERSION 3.14.0)
 project(notcurses VERSION 2.0.4
   DESCRIPTION "Blingful UI for modern terminal emulators"

doc/examples/book.toml

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+[book]
+authors = ["nick black"]
+language = "en"
+multilingual = false
+src = "src"
+title = "A Gentle Introduction to Notcurses"

doc/examples/src/SUMMARY.md

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+# Summary
+
+- [Chapter 1](./chapter_1.md)

doc/examples/src/chapter_1.md

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+# Chapter 1
+
+Notcurses is a library for terminal applications—programs which do not require
+a GUI environment, and write output as cells rather than pixels. Within a GUI
+environment, such programs run in a *terminal emulator*; they can also run
+on a *virtual console*, a *pseudoterminal* (such as those used by `ssh`), or
+even a true hardware terminal. It is inspired by the X/Open Curses
+specification, though it is (by necessity) not source-compatible with that API.
+
+Terminal applications emit a stream of *code points*. Code points index into
+the terminal's *character set*; visual characters are run through a font engine
+to produce *glyphs*, whereas *escape sequences* facilitate in-band control of
+the output and operation of the terminal, including changing presentation style
+and moving the cursor. A major function of Notcurses is to portably and
+efficiently emit the sequences necessary to effect higher-level client goals.
+
+Notcurses offers two major modes of operation:
+* **Direct mode** can be used together with standard I/O. It is primarily meant
+  to enhance simple scrolling applications via coloring and styling, though it
+  can also move the cursor, read raw keyboard input, and render media. Use
+  direct mode if you intend to primarily output through standard library
+  functions such as `printf()`. Direct mode uses `struct ncdirect`s.
+* **Fullscreen mode** facilitates more complex Text User Interface applications.
+  These applications maintain virtual state in the form of an ordered stack of
+  `struct ncplane`s; when they're ready, the visible area is redrawn. It can
+  provide much greater performance than direct mode, but does not tolerate the
+  use of standard I/O. Fullscreen mode uses `struct notcurses`.
+
+Whichever mode is used, it is essential to destroy all Notcurses contexts upon
+program exit, or the terminal can be left in an undesirable state. By default,
+Notcurses registers handlers for most fatal signals, to destroy its own
+contexts. On a typical exit, the user must destroy these contexts.
+
+Notcurses does not strictly require a terminal device for input or output; it
+can be freely redirected to arbitrary character devices or files. When not
+connected to a terminal device, many escapes will not be generated.
+
+Whether using fullscreen or direct mode, there are a few technical minutia
+almost every Notcurses program will want to do early on:
+
+* Call `setlocale()` to modify the program's POSIX locale, usually based
+  on the `LANG` environment variable. This is necessary to place the program
+  in UTF-8 mode, which is necessary for optimal Notcurses operation [^Unless
+  the `INHIBIT_SETLOCALE` flag is used, Notcurses will handle this for you
+  if you don't do it, but it's ideally done as one of the very first steps of
+  your program.].
+* Mask out `SIGWINCH`, especially if you intend to create any threads. This is
+  necessary to ensure WINdow CHange notifications go to the desired thread.