Clang Format (#514)

* Apply clang-format

* Fixed conflict between "print.h" and <print.h>

print.h and print.cpp are not used.

* machine.h: clang-format off is unnecessary

* ifdef ARDUINO_ARCH_ESP32 is unnecessary

and causes irritiating indentation of other includes

* Revert formatting of nofile.h

But leave pragma changes.

* Fix nofile.h again

* Some files were not formatted ...

and .clang-format needed to be tweaked to
give the same results with clang-format v6 and v10

* clang-format v6 vs v10 compatibility

CodingStyle.md

@@ -0,0 +1,80 @@
+# Coding style guidelines
+
+While most software developers have a strong opinion about coding 
+style and conventions, the general agreement is that having a single 
+coding style in your project is beneficial for the readability and 
+maintainability. 
+
+Coding style of this project is enforced through `.clang-format`. 
+Most IDE's nowadays pick up the clang-format file automatically. If
+this is not the case, please run it manually before committing code.
+
+Note that different IDE's are compiled against different versions of 
+clang-format. This clang-format file is created in such a way, that 
+it should work with most IDE's out-of-the-box, and can apply changes 
+when the file is saved.
+
+There may be violations of these guidelines in the code, due to
+historical reasons or, in rare instances, other considerations.
+We intend to fix such violations; patches that correct them
+are most welcome - but should be tested carefully across the
+supported compilation environments (Arduino and platformio).
+
+## Guidelines 
+
+A few guidelines need to be taken into consideration while using 
+clang-format:
+
+1. Include order and `".."` vs `<...>` matters. Clang-format 
+   automatically re-orders your include files. This configuration 
+   is created in such a way that header file includes always add
+   the minimum number of implicit dependencies. If this generates 
+   problems, you should be fixing your includes, instead of disabling
+   clang-format.
+2. Preprocessor commands are not formatted nicely in some cases.
+   This can hurt readibility in rare cases, in which case it's 
+   okay to disable clang-format temporarily with 
+   `// clang-format off` and `// clang-format on`. Most notably, 
+   machine definitions should have clang-format off.
+3. Use `#pragma once` in all header files. The reason is that 
+   preprocessor `#ifdef`s are nested automatically, which making 
+   things messy when using the alternative.
+
+## Classes and namespaces
+
+Filenames should correspond with clas names, folder names should 
+correspond with namespace names. This implies that a file should 
+have a single class.
+
+## Naming
+
+- Class names and namespace names are named `CamelCase`. Note that 
+  class and namespace names should only start with an `_` if they are 
+  (A) not in the global namespace and (b) should otherwise start with a digit.
+  For example `_10VSpindle`.
+- Class member functions should be `snake_case`
+- Class member variables should be `_snake_case` with a leading `_`.
+ 
+Namespaces should have classes, and classes should have members. Avoid
+using functions that have no class attached to them.
+
+## Using namespace
+
+- `using namespace` is not allowed in header files, except when 
+  using it in the body of a function.
+- Try to be conservative with `using namespace` in cpp files. 
+  Prefer to use it in a function body whenever possible for clarity
+  what is used where.
+
+## Including files
+
+- It's a good practice to include just what you need. In general,
+  try to include as much as possible in the cpp file, and as little 
+  as possible in the header file.
+- A CPP file should normally include the corresponding header file 
+  first (e.g. `WebSettings.cpp` should include `WebSettings.h`)
+  and then everything else.
+- When including a system or library file, use `<...>` syntax; 
+  when including a local file, use `"..."` syntax. Some IDE's
+  actually have trouble compiling if not done correctly.
+- Never include a cpp file; always header files!