Fix output directory for globs

[AnthonyGrondin]

This is a partial fix for #127.

Previously, user specified globs were placed in the root directory of dummy C project, rather than in the created folder.

Partial fix

This is a partial fix, because the glob works with wildcards like certs/*, but doesn't work with wildcards like certs*, the crate globwalk used for finding files doesn't return the right list of files when using certs*.
We have two choices:

1. Edit the README.md to change mentions of foo* and bar* to foor/* and bar/*
2. Fix the way embuild, the crate used for copying files, finds files.
   https://github.com/esp-rs/embuild/blob/5e12da302f372c05d20a149b00eca1befde185f6/src/build.rs#L95-L114

Example

ESP_IDF_GLOB_CRT_BASE = { value = ".", relative = true}
ESP_IDF_GLOB_CRT_CERT = "certs/certificate.pem"

.
├── Cargo.lock
├── Cargo.toml
├── certs/
     └── certificate.pem
├── README.md
├── rust-toolchain.toml
├── sdkconfig.defaults
└── src
     └── main.rs

This will put the file certificate.pem in the directory certs at the root of the dummy C project

.
├── bindings.rs
├── build
│   └── ...
├── certs
│   └── certificate.pem
├── CMakeLists.txt
├── esp-idf-build.json
├── gen-sdkconfig.defaults
├── main.c
└── sdkconfig

[N3xed]

Thanks for the (partial) fix!