Improve show of tables

[nickrobinson251]

Before (on main):

julia> net.multi_terminal_dc
MultiTerminalDCLines with 0 records, 1 columns:


julia> net.generators
Generators with 3 records, 20 columns:
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
    i   id      pg     qg     qt     qb       vs    ireg  mbase   zr   zx   rt   xt  gtap  stat  rmpct     pt   pb  oi   fi
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  111   ST     0.0    0.0  110.0    0.0  1.01375  334153  161.0  0.0  1.0  0.0  0.0   1.0  true  200.0   90.0  0.0   1  1.0
 -112  PV      3.1  -91.0   91.0  -31.0  1.14634       0  175.0  0.0  1.0  0.0  0.0   1.0  true  300.0   91.0  0.0   2  1.0
  113    1  313.01  82.29  147.0  -72.0   1.1233       0  380.0  0.0  1.0  0.0  0.0   1.0  true   55.1  229.0  0.0   2  1.0
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

After (this PR):

julia> net.multi_terminal_dc
MultiTerminalDCLines with 0 records

julia> net.generators
Generators with 3 records, 20 columns:
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
    i   id      pg      qg     qt     qb       vs    ireg  mbase   zr   zx   rt   xt  gtap  stat  rmpct     pt   pb  oi   fi
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  111   ST    0.0     0.0   110.0    0.0  1.01375  334153  161.0  0.0  1.0  0.0  0.0   1.0  true  200.0   90.0  0.0   1  1.0
 -112  PV     3.1   -91.0    91.0  -31.0  1.14634       0  175.0  0.0  1.0  0.0  0.0   1.0  true  300.0   91.0  0.0   2  1.0
  113    1  313.01   82.29  147.0  -72.0  1.1233        0  380.0  0.0  1.0  0.0  0.0   1.0  true   55.1  229.0  0.0   2  1.0
─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

[codecov-commenter]

Codecov Report

Merging #49 (972b997) into main (5bbeeef) will decrease coverage by 0.28%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
- Coverage   94.26%   93.98%   -0.29%     
==========================================
  Files           3        3              
  Lines         279      266      -13     
==========================================
- Hits          263      250      -13     
  Misses         16       16              

Impacted Files	Coverage Δ
src/types.jl	95.50% <100.00%> (ø)
src/parsing.jl	98.79% <0.00%> (-0.09%)	⬇️

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