Describe what each python module does

tools/README.md

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+# Mbed OS Build Tools
+
+This directory contains the python tools used for building Mbed OS and
+Mbed 2. 
+
+Quick navigation:
+
+| file/directory        | What it do                                     |
+|-----------------------|------------------------------------------------|
+| `build.py`            | implementation of `mbed compile --library`     |
+| `build_api.py`        | full-project build operations                  |
+| `build_release.py`    | CLI for making an mbed 2 release               |
+| `build_travis.py`     | travis testing script                          |
+| `config`              | implementation of Config System                |
+| `debug_tools`         | Crash log parsing                              |
+| `default_settings.py` | Default version of project local `settings.py` |
+| `detect_targets.py`   | implementation of `mbed detect`                |
+| `device_management.py`| implementation of `mbed device-management`     |
+| `export`              | Export plugins and API for woking with them    | 
+| `flash_algo`          | CMSIS flash algorithm parser                   |
+| `get_config.py`       | implementation of `mbed compile --config`      |
+| `host_tests`          | location of pre-htrun host tests               |
+| `importer`            | code importer for use with CMSIS, TFM/PSA etc. |
+| `libraries.py`        | constants for building mbed 2 libraries        |
+| `make.py`             | implementation of `mbed compile`               |
+| `memap.py`            | map file parser and sumary generator           |
+| `notifier`            | API for seting compile status to a frontend    |
+| `options.py`          | Default option parser and option utilities     |
+| `paths.py`            | constants for many paths used                  |
+| `profiles`            | location of the default build profiles         |
+| `project.py`          | implementation of `mbed export`                |
+| `psa`                 | PSA                                            |
+| `regions.py`          | merging from managed bootloader mode           |
+| `resources`           | scans directories for files used in a project  |
+| `run_icetea.py`       | implementation of `mbed test --icetea`         |
+| `settings.py`         | project specific settings from env vars        |
+| `singletest.py`       | location of pre-greentea greentea              |
+| `targets`             | target description reader and post-build steps |
+| `test`                | unit tests for tools                           |
+| `test_api.py`         | part of pre-greentea greentea                  |
+| `test_configs`        | configuration files used by `mbed test`        |
+| `test_db.py`          | part of pre-greentea greentea                  |
+| `test_exporters.py`   | part of pre-greentea greentea                  |
+| `test_mysql.py`       | part of pre-greentea greentea                  |
+| `test_webapi.py`      | part of pre-greentea greentea                  |
+| `tests.py`            | implementation of `mbed test --greentea`       |
+| `toolchains`          | API for calling the selected compiler          |
+| `upload_results.py`   | part of pre-greentea greentea                  |
+| `utils.py`            | General purpose utilities like file moving     |
+