Add driver slot documentation

Driver slots had a structure before, but now, it's defined how the
layout should be done. The design was also changed significantly, so
the PCI and ACPI drivers have to be changed now.

i386/docs/drivers/slot-structure.md

@@ -0,0 +1,73 @@
+# Nightloader Driver Structure
+
+This documentation file explains the format of a native driver slot
+for the Nightloader on the i386 architecture.
+
+| Offset | Length    |        Name of Field              |
+| ------ | --------- | --------------------------------- |
+|   0    |     8     |  Driver Identifier                |
+|   8    |     2     |  Format Version                   |
+|   10   |     2     |  Driver Version                   |
+|   12   |     2     |  Number of Functionalities        |
+|   16   |     4     |  Functionality Table Offset       |
+
+1. Driver Identifier  
+   The driver identifier is used to uniquely identify a driver. It can
+   be chosen by a driver's developer, but should suggest what kind of
+   driver is contained in that slot, for the sake of clarity.
+
+2. Format Version  
+   The version of the driver slot's standardized structures such as
+   the rest of the header, the functionality table and others that
+   the future might bring.  
+   The first byte of this structure tells the major version, the
+   second one tells the minor version. No version patches are needed.
+
+3. Driver Version  
+   Version of the driver, as seen by the driver's developer.  
+   The first byte of this structure should be the major version, the
+   second one the minor version. No version patches are needed.
+   
+4. Number of Functionalities  
+   How many entries the functionality table contains. The table of
+   functionalities contains functions with standardized arguments,
+   actions and return types for interfacing with the driver.
+
+5. Functionality Table Offset  
+   Offset *from the start of the driver slot* to the functionality
+   table. It may be wise to keep this a bit further away from the
+   header to prevent the need for more changes if the header structure
+   changes in a future version.
+
+## Functionality Structure
+
+Functionalities in the functionality table have a structure defined in
+the following table:
+
+| Offset |  Length   |  Name of Field                    |
+| ------ | --------- | --------------------------------- |
+|   0    |     2     |  Function Category                |
+|   2    |     2     |  Exact Function                   |
+|   4    |     4     |  Function Pointer                 |
+
+> The functionality table as it is found in any correct driver is a
+> tightly packed array of those structures with as many elements as
+> were promised in the corresponding header field.
+
+## Driver Functionality Categories
+
+The table below contains links to the driver functionality categories:
+
+|  Id    |  Category                                     |
+| ------ | --------------------------------------------- |
+|  0x1   |  [Basic Text](./textwriter-functions.md)      |
+|  0x2   |  [Text Window](./window-functions.md)         |
+|  0x3   |  [Logger](./logger-functions.md)              |
+|  0x4   |  [Pixel Graphics](./graphic-functions.md)     |
+|  0x5   |  [Pixel Fonts](./pixel-font-functions.md)     |
+|  0x10  |  [PCI](./pci-functions.md)                    |
+|  0x11  |  [PCIe](./pcie-functions.md)                  |
+|  0x12  |  [NVMe](./pcie-functions.md)                  |
+|  0x20  |  [USB](.usb/-functions.md)                    |
+|  0x30  |  [Storage](./storage-functions.md)            |
+|  0x40  |  [Filesystem](./filesystem-functions.md)      |