Updating issue and PR templates

[lbergelson]

Updating the issue and PR templates to make the clearer and more helpful as guidelines to submitters.

[codecov-io]

Codecov Report

Merging #1393 into master will increase coverage by 0.206%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #1393       +/-   ##
===============================================
+ Coverage     68.017%   68.223%   +0.206%     
- Complexity      8361      8653      +292     
===============================================
  Files            571       571               
  Lines          33877     34424      +547     
  Branches        5662      5872      +210     
===============================================
+ Hits           23042     23485      +443     
- Misses          8645      8715       +70     
- Partials        2190      2224       +34

Impacted Files	Coverage Δ	Complexity Δ
...main/java/htsjdk/variant/vcf/AbstractVCFCodec.java	76.218% <0%> (+0.573%)	100% <0%> (+2%)	⬆️
...dk/variant/variantcontext/GenotypeLikelihoods.java	85.827% <0%> (+0.856%)	92% <0%> (+18%)	⬆️
...va/htsjdk/tribble/TribbleIndexedFeatureReader.java	71.978% <0%> (+1.648%)	26% <0%> (ø)	⬇️
.../htsjdk/variant/variantcontext/VariantContext.java	80.545% <0%> (+2.831%)	443% <0%> (+197%)	⬆️
...n/java/htsjdk/variant/variantcontext/Genotype.java	62.917% <0%> (+3.881%)	125% <0%> (+45%)	⬆️
...java/htsjdk/variant/variantcontext/CommonInfo.java	53.939% <0%> (+6.076%)	68% <0%> (+21%)	⬆️
src/main/java/htsjdk/variant/vcf/VCFUtils.java	50.532% <0%> (+6.087%)	26% <0%> (+9%)	⬆️