The 'build' directory should be created before starting docker.
If not it will be created as root.

Also add mapping for the directory in docker.

Currently create the directory in the target until there is a directory
creation target.

The 'build' directory should not be tracked by git.

This introduces a new environment variable for a common directory
that holds all output of the build process, such as application or
package binaries. This would also allow to easily redirect output
to any other location, e.g. for out-of-source builds.

Improved docs on module name uniqueness

drivers/adxk345: include copy of params in dev struct

cpu/atmega_common/uart: Comment why brr calc is different from datasheet

gnrc_netif: add l2addr members to doc

board/z1: Fix BTN0_PIN

drivers/lsm6dsl: eliminate and correct casts

drivers/lsm303dlhc: correct cast of phydat_t*

tests/driver_at86rf2xx: eliminate cast

drivers/ccs811: remove unnecessary casts

net/coap: improve message code macros

The `l2addr` and `l2addr_len` members of the `gnrc_netif_t` struct did
not show up in the rendered documentation.

 gnrc_sixloenc: introduce pseudo-module to send 6Lo frames over Ethernet

gnrc: make titles of NETAPI command documentation more specific

tests/xtimer_drift: increase priority of worker

gnrc_ipv6: make gnrc_netapi documentation more detailed

The brr calculation on the datasheet is different than what is implmented.
This is intentional since it provides better rounding due to truncation.
There was no comment explaining that so this comment should prevent confusion.

drivers/ads101x: eliminate casts

The read functions have a mpu9150_results_t* argument which is a
struct with 3 int16_t members. Thus we should cast res->val instead of
just res.

The read functions have a mma8x5x_data_t* argument which is a
struct with 3 int16_t members. Thus we should cast res->val instead of
just res.

The read functions have a mag3110_data_t* argument which is a
struct with 3 int16_t members. Thus we should cast res->val instead of
just res.

The read functions have a mma7660_data_t* argument which is a
struct with 3 int16_t members. Thus we should cast res->val instead of
just res.

This follows the usual convention of having the whole params in the device
struct instead of a pointer-to. This also eliminates the need to cast a
const to a non-const pointer in the init function.

The read functions have a lsm303dlhc_3d_data_t* argument which is a
struct with 3 int16_t members. Thus we should cast res->val instead of
just res.

Converting phydat_t* to lsm6dsl_3d_data_t* is not correct, but it happened
to just work because the first struct member of phydat_t will be used.

Furthermore, casting &res[0] to int16_t* is wrong. Again, it just happened
to work.

cpu/esp32: Fixes the maximum packet size of 255 bytes in the esp_eth netdev driver of ESP32 mcu.