[Tcs] [VOTEv2] Change export directory guidelines (was Fix avatar export 'working directory' wording)

[John Smith]

This is v2 of the pull request #23, now #24 on GH:
https://github.com/Tox/Tox-Client-Standard/pull/24
The v1 had some serious problems, as pointed out by @nurupo

I've made some changes from "working directory" to "export directory" 
It's now recommended that users can choose where they want to export, 
and it's required that the export directory be accessible to the user.
I haven't moved to required hashing the PK in avatar file names
since that wasn't the main issue in #22, but this could be discussed later.

Please start voting on this pull request.
---
diff --git a/data_storage/export_format.md b/data_storage/export_format.md
index 64cf6e5..fde8135 100644
--- a/data_storage/export_format.md
+++ b/data_storage/export_format.md
@@ -1,22 +1,28 @@
 Export Format
 -------------
 
-- **5.1.1** ![](/badge/req.png) A Toxcore data file saved in the root of the client's
-  working directory, with the file name `<profile_name>.tox`
+- **5.1.1** ![](/badge/req.png) The client will export files relative to a folder called
+  the export folder, which must be in a location accessible to the user.
 
-- **5.1.2** ![](/badge/req.png) If the client supports user avatars, they will be stored
-  under the `avatars/` directory in the root of the client's working directory.
+- **5.1.2** ![](/badge/rec.png) The user should be able to choose the location
+  of the export folder.
 
-- **5.1.3** ![](/badge/req.png) Avatars are named according to the following format:
+- **5.1.3** ![](/badge/req.png) A Toxcore data file saved in the root of the
+  export folder, with the file name `<profile_name>.tox`.
+
+- **5.1.4** ![](/badge/req.png) If the client supports user avatars, they will be stored
+  under the `avatars/` directory in the root of the export folder.
+
+- **5.1.5** ![](/badge/req.png) Avatars are named according to the following format:
   `PK.png`, where PK is the 64-character hexadecimal public key of its owner.
 
 - An example file hierarchy:
 
   ```
   +-----------------------------------------------------------------------------------+
-  |   / (client working dir)                                                          |
+  |   / (export folder)                                                               |
   |    |                                                                              |
-  |    +-- tox_save.tox                                                               |
+  |    +-- profile_name.tox                                                           |
   |    +-- avatars/                                                                   |
   |         |                                                                         |
   |         +-- E62DACF4C0DD23156F745874CBDBCD3D3E356F51C67921F7D91A7938CEB87933.png  |