Fix compilation on no_std.

[reitermarkus]

#42 broke compilation without any features, since Vec isn't available for the into_packet_vec function.

[timbod7]

I'm struggling to get this to work on a cortex-m system. I've got this in cargo.toml:

ublox = { version = "0.4.2", features = []}

[patch.crates-io]
ublox = { git = 'https://github.com/reitermarkus/ublox', branch='no-std'}

but I get pages and pages of errors, that start off like this:

~/gps-tracker/firmware$ cargo build --release
   Compiling ublox v0.4.2 (https://github.com/reitermarkus/ublox?branch=no-std#c1a02fb3)
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7em-none-eabihf` target may not support the standard library
  = note: `std` is required by `ublox` because it does not declare `#![no_std]`

error: cannot find attribute `derive` in this scope
 --> /home/timd/.cargo/git/checkouts/ublox-a2964f230499e503/c1a02fb/ublox/src/error.rs:3:3
  |
3 | #[derive(Debug)]
  |   ^^^^^^
  |
  = note: consider importing this attribute macro:
          core::prelude::rust_2021::derive

error: cannot find macro `write` in this scope
  --> /home/timd/.cargo/git/checkouts/ublox-a2964f230499e503/c1a02fb/ublox/src/error.rs:13:42
   |
13 |             MemWriterError::Custom(e) => write!(f, "MemWriterError: {}", e),
   |                                          ^^^^^
   |
   = note: consider importing this macro:
           core::write

error: cannot find attribute `derive` in this scope
  --> /home/timd/.cargo/git/checkouts/ublox-a2964f230499e503/c1a02fb/ublox/src/error.rs:22:3
   |
22 | #[derive(Debug, PartialEq, Eq)]
   |   ^^^^^^
   |
   = note: consider importing this attribute macro:
           core::prelude::rust_2021::derive

error: cannot find macro `write` in this scope
  --> /home/timd/.cargo/git/checkouts/ublox-a2964f230499e503/c1a02fb/ublox/src/error.rs:46:61
   |
46 |             ParserError::InvalidChecksum { expect, got } => write!(
   |                                                             ^^^^^
   |
   = note: consider importing this macro:
           core::write
...

Any pointers as to what I'm doing wrong?

[reitermarkus]

@timbod7, you need

ublox = { version = "0.4.2", default-features = false }

[timbod7]

Excellent - thanks so much.

[reitermarkus]

@lkolbly, can this be merged and could you please respond in #52 if you get a chance?