Add gbk2pf converter.

[ArnaudBelcour]

As genbank formats created by different tools are different, we can have errors during PathoLogic. To solve these errors, we could convert genbank into PathoLogic Format.

The idea is to add a new argument:

mpwt gbk2pf -i input_folder -o output_folder --cpu number_cpu

This command takes as argument a folder containing the genbank (in the same structure than the input_folder of mpwt -f) and an output folder. It will then generates the PathoLogic Format files from the genbank.

[ArnaudBelcour]

It could also be useful to have a gff2pf converter.

So I will create a new command:

mpwt topf -i input_folder -o output_folder

[ArnaudBelcour]

Added in #32 but need more polishing in 0.5.3.

[ArnaudBelcour]

Fix some issues but it needs more testing and polishing in 0.5.4.