Basic mass/fragment calculators in alphabase

[jalew188]

In constants sub-module:

• element.ipynb stores base chemical element information.
• aa.ipynb processes any amino acid related information, including fast ASCII code-based sequence mass calculation.
• modification.ipynb processes any modification related information, including mass and modloss mass calculation.

In peptide sub-module:

• fragment.ipynb processes any fragment information, including a fast way to generate fragment mass (b,y,b-modloss,...) dataframe

[jalew188]

We can review these codes when merging into main