Add string and chemical formulae utility functions

[sjdaines]

"""
    parse_number_name(nname::AbstractString) -> (number, name)

Parse a string of form "-1*A"

"""

"""
    ChemistryUtils.parse_chemical_formula(formula::AbstractString) -> element_counts::OrderedDict{Symbol, Float64}

Parse a chemical formula into a Dict of element counts 
"""

"""
    ChemistryUtils.calc_molar_mass(element_counts::AbstractDict) -> molar_mass::Float64

Add up element masses to get molar mass (g)
"""

"""
    Constants.STANDARD_ATOMIC_WEIGHTS

IUPAC recommended values of relative atomic masses of sources in the local environment of the Earth's crust and atmosphere (ie with Earth-specific isotope composition)
"""

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 75.00000% with 10 lines in your changes missing coverage. Please review.

Project coverage is 53.98%. Comparing base (9135e8a) to head (b770312).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/utils/StringUtils.jl	68.75%	5 Missing ⚠️
src/Model.jl	0.00%	2 Missing ⚠️
src/Types.jl	0.00%	2 Missing ⚠️
src/utils/ChemistryUtils.jl	94.44%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #141      +/-   ##
==========================================
- Coverage   54.88%   53.98%   -0.91%     
==========================================
  Files          39       41       +2     
  Lines        4267     4007     -260     
==========================================
- Hits         2342     2163     -179     
+ Misses       1925     1844      -81     

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