Fbpic

This is bug-fix release. It fixes two bugs that were introduced in version

This version incorporates various new features, optimizations and bug fixes.
See below for a details.

New features:
- The messages printed by FBPIC to the terminal have been improved.
The `Simulation` class now supports a `verbose_level` argument, in order to
choose the desired level of information [158](https://github.com/fbpic/fbpic/pull/158).
- More self-consistent initialization of the laser field [150](https://github.com/fbpic/fbpic/pull/150).
The laser initialization now supports arbitrary laser profiles and is always exactly
divergence-free, even for MPI-decomposed simulations. More laser profiles
will be implemented and documented in the next release.

New optimizations:
- The code performs fewer Hankel transforms per iteration, and is thus faster [161](https://github.com/fbpic/fbpic/pull/161).
- Faster functions for removal/addition of particles on GPU [179](https://github.com/fbpic/fbpic/pull/179)

Bug fixes:
- The position where plasma starts to be injected (for simulations with moving window,
featuring no plasma initially in the box) has been corrected. This mainly affects boosted-frame
simulations. [160](https://github.com/fbpic/fbpic/pull/160)
- When restarting simulations from checkpoints, there was a bug in the particle
weights, which is now fixed. [178](https://github.com/fbpic/fbpic/pull/178)
- The current and charge density are now written in the fields diagnostics
for iteration 0, whereas they were previously set to 0 in the diagnostics for this iteration.
[178](https://github.com/fbpic/fbpic/pull/178)
- The boosted-frame particle diagnostics used to fail in some cases on GPU
due to an out-of-bound access, which is now fixed. [169](https://github.com/fbpic/fbpic/pull/169)

Changes related to the installation process:
- FBPIC can now use numba 0.36 with threading [167](https://github.com/fbpic/fbpic/pull/167) and [#170](https://github.com/fbpic/fbpic/pull/170).
- FBPIC is now able to load MKL on Windows [177](https://github.com/fbpic/fbpic/pull/177) and has better support when MKL fails to load [#154](https://github.com/fbpic/fbpic/pull/154).
- FBPIC can now run without having MPI installed (for single-GPU or single-CPU node simulations) [143](https://github.com/fbpic/fbpic/pull/143)

This is a bug-fix release. It corrects an important bug that was introduced in version 0.6.1 for the Hankel transform on GPU.

This version allows FBPIC to run without `mpi4py` installed, in the case of
single-proc simulations.

In addition, the current deposition on CPU, as well as the Hankel transform
on CPU and GPU have been optimized and should have significantly faster
execution time.

Finally, FBPIC now prints a message during just-in-time compilation.

This version allows FBPIC to use the MKL library for FFTs, on CPU. In most cases,
this will result in faster code execution compared to the FFTW library, especially
on CPUs with a large number of cores. FFTW can still be used with FBPIC if MKL is unavailable.

In addition, this version optimizes the number of thread per block on GPU for
costly operations, which should also result faster code execution.

This is a bug-fix release. It fixes the initial space-charge calculation by ensuring that:
- this calculation does not erase any pre-existing field (e.g. laser field)
- this calculation gives correct results for multi-CPU/multi-GPU simulations as well