Auto merge of #92 - matthiasbeyer:doc-define-modules, r=matthiasbeyer

Doc define modules

Includes definition of runtime library.

doc/src/03100-lib-rt.md

@@ -0,0 +1,73 @@
+# librt {#sec:librt}
+
+The runtime library provides types and functions which MUST be used by the
+modules to implement the commandline interface, configuration file parsing and
+logging.
+
+The runtime library provides basic functionality for configuration file parsing
+and logging setup.
+The runtime library also provides helper functions for building a commandline
+interface.
+
+## Configuration file {#sec:librt:cfg}
+
+The runtime library SHOULD read the configuration file, if it can be found.
+If the configuration file cannot be found, the following variables are set to
+their default values as shown in @tbl:librt:cfg:defaultvalues.
+
+| Variable       | Value                |
+| :------------- | :------------------- |
+| verbosity      | false                |
+| debugging      | false                |
+| store location | `$HOME/.imag/store/` |
+
+Table: Default values for configuration if configuration file unavailable
+{#tbl:librt:cfg:defaultvalues}
+
+### Location of the configuration file {#sec:librt:cfg:location}
+
+For the configuration file is searched at the following locations:
+
+1. Path: `$HOME/.imag/config`
+1. Path: `$HOME/.imag/config.toml`
+1. Path: `$HOME/.imag/imagrc`
+1. Path: `$HOME/.imag/imagrc.toml`
+1. Path: `$XDG_CONFIG_DIR/imag/config`
+1. Path: `$XDG_CONFIG_DIR/imag/config.toml`
+1. Path: `$XDG_CONFIG_DIR/imag/imagrc`
+1. Path: `$XDG_CONFIG_DIR/imag/imagrc.toml`
+1. Path in the environment variable `$IMAG_CONFIG`
+
+If neither of these configuration files are found, the program MUST USE the
+default values for the minimum required variables
+(@tbl:librt:cfg:defaultvalues).
+
+### Contents of the configuration file {#sec:librt:cfg:contents}
+
+The contents of the configuration file MUST BE encoded in Unicode UTF-8.
+The contents of the configuration file are structured as TOML, regardless of the
+file extension.
+
+The configuration file contains several sections:
+
+1. The `base` section, which contains basic variables
+   (@tbl:librt:cfg:contents:base)
+1. The `modules` section, which contains a section for each module.
+1. The `store` section, which contains configuration on the behaviour of the
+   store (@tbl:librt:cfg:contents:store)
+
+| Variable       | Type    |
+| :------------- | :------ |
+| verbosity      | boolean |
+| debugging      | boolean |
+| store location | Path    |
+
+Table: "Base" variables in the configuration file {#tbl:librt:cfg:contents:base}
+
+
+| Variable  | Type    | Meaning                                          |
+| :-------- | :------ | :----------------------------------------------- |
+| git-vcs   | boolean | Whether the store is version controlled with git |
+
+Table: "store" variables in the configuration file {#tbl:librt:cfg:contents:store}
+

doc/src/06000-modules.md

@@ -1,2 +1,20 @@
 # Modules {#sec:modules}
 
+A module is a functionality of the program.
+
+A module MAY store data in the store (@sec:thestore).
+It MAY include user input in the data it stores in the store.
+A module MUST HAVE a commandline interface, though a module always consists of
+two parts:
+
+- A Library
+- A Binary, which
+    * is executable by the user
+    * implements a commandline frontend to the libray of the module
+
+By definition, the Binary depends on the Library.
+By definition, the Library depends on the libstore (@sec:libstore).
+
+A module MUST use the runtime library to implement the commandline
+interface as defined in @sec:librt.
+