Additional features (in development)

[rikutakei]

Temporary merge of the additional LZ features, including:

• labelling multiple secondary SNPs (by passing it a vector of variants)
• remove code to calculate offsets for label positioning (use pos argument instead)
• allow multiple summary stats in a single plot and adjust output size accordingly
• function to read PLINK clump file
• allow string representation of P, and -log10P calculation for very small P
• some preliminary scripts for calculating LD and generating LZ plots in parallel