Start CODINGSTYLE document and add table with abbreviations

To get consistent and readable code let's try to advertise some common
abbreviations.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>

CODINGSTYLE.md

@@ -0,0 +1,46 @@
+Coding guidelines for s390-tools
+================================
+
+For s390-tools the preferred language is C. We provide libraries, e.g. libutil
+that should be used by all tools if possible.
+
+The coding style is based on the Linux kernel guidelines. Therefore, use
+the checkpatch tool for verification before you submit a patch:
+
+ - https://github.com/torvalds/linux/blob/master/scripts/checkpatch.pl
+
+Below we describe some additional things that we want you to consider when
+writing new code for s390-tools.
+
+This package started in 2001 and has a long "tradition" - therefore, older tools
+might not follow all recommendations. Note that when changing existing code,
+consistency could have priority over applying rules.
+
+Standard abbreviations
+----------------------
+
+The abbreviations below are recommended to be used in the source code.
+
+| __Short Name__  | __Long Name__                                     |
+|:----------------|:--------------------------------------------------|
+| attr            | Attribute                                         |
+| blk             | Block                                             |
+| buf             | Buffer                                            |
+| col             | Column                                            |
+| count           | Count                                             |
+| desc            | Description                                       |
+| dir             | Directory                                         |
+| fd              | File descriptor (open)                            |
+| fp              | File pointer (fopen)                              |
+| len             | Length                                            |
+| lib             | Library                                           |
+| mod             | Module                                            |
+| nr              | Number                                            |
+| parm            | Parameter                                         |
+| path            | File path                                         |
+| ptr             | Pointer                                           |
+| rc              | Return code                                       |
+| size            | Size                                              |
+| src             | Source                                            |
+| str             | String                                            |
+| sym             | Symbol                                            |

CONTRIBUTING.md

@@ -54,12 +54,5 @@ Submitting code
 ---------------
 The preferred way is to create a github pull request for your code.
 
-Coding guidelines
------------------
-For s390-tools the preferred language is C. We provide libraries, e.g. libutil
-that should be used by all tools if possible.
-
-The coding style is based on the Linux kernel guidelines. Therefore, use
-the checkpatch tool [1] for verification before you submit a patch.
-
-[1] https://github.com/torvalds/linux/blob/master/scripts/checkpatch.pl
+Before you submit your code please consider our recommendations in the
+[CODINGSTYLE](CODINGSTYLE.md) document.

README.md

@@ -11,6 +11,7 @@ The package also contains the following files:
  * [LICENSE](LICENSE): The MIT license that applies to this package
  * [CHANGELOG](CHANGELOG.md): The history of s390-tools versions
  * [AUTHORS](AUTHORS.md): A list of all authors of the s390-tools package
+ * [CODINGSTYLE](CODINGSTYLE.md): Recommendations for writing s390-tools code
 
 Package contents
 ----------------